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GATA factors are essential transcription factors for embryonic development that broadly control the transcription of other genes. This study aimed to examine GATA2 protein localization in mouse embryos at the 2-cell stage, when drastic transformation in gene expression occurs for subsequent development in early embryos. We first analyzed GATA2 localization in 2-cell embryos at the interphase and mitotic phases by immunofluorescence analysis. In the interphase, GATA2 protein was localized in the nucleus, as a common transcription factor. In the mitotic phase, GATA2 protein was observed as a focally-aggregated spot around the nucleus of each blastomere. To explore the relationship between GATA2 protein localization and cell cycle progression in mouse 2-cell stage embryos, GFP-labeled GATA2 protein was overexpressed in the blastomere of 2-cell embryos. Overexpression of GFP-labeled GATA2 protein arrested cellular mitosis, focally aggregated GATA2 protein expression was not observed. This mitotic arrest by GATA2 overexpression was not accompanied with the upregulation of a 2-cell stage specific gene, murine endogenous retrovirus-L. These results suggest that GATA2 protein localization changes dynamically depending on cell cycle progression in mouse 2-cell embryos; in particular, focally aggregated localization of GATA2 in the mitotic phase requires appropriate cell cycle progression.

We examined the effect of the timing of removing cumulus cells surrounding porcine oocytes from small follicles (SFs, < 3 mm in diameter) and medium follicles (MFs; 3-6 mm in diameter) on the meiotic and developmental competence of the oocytes. Cumulus-oocyte complexes (COCs) were collected from SFs and MFs, and the oocytes were denuded at 0, 20, and 44 h after the start of in vitro maturation (IVM), and the meiotic progression of the oocytes was assessed at the end of the IVM period. The incidence of mature oocytes was significantly affected by both the origin of the COCs and the time when the oocytes were denuded. Although the percentage of mature oocytes was always higher when the COCs were collected from MFs than that when the COCs were collected from SFs, the maturation rate was significantly higher when the oocytes were denuded at 20 h than when they were denuded at 44 h after the start of IVM. When the mature oocytes were activated electrically, the developmental competence of the oocytes denuded at 20 and 44 h to reach the blastocyst stage did not differ, whereas the competence of the MF-derived oocytes was significantly higher than that of SF-derived oocytes. When the intracellular cAMP and cGMP levels in SF-derived oocytes were examined at 24 h of IVM, the levels of both were significantly decreased only in the oocytes denuded at 20 h. In conclusion, denuding oocytes at 20 h of IVM caused a significant reduction in ooplasmic cAMP and cGMP levels and increased the meiotic competence of the oocytes without any reduction in blastocyst formation, even in the case of SF-derived oocytes.

Changes in the intracellular concentration of calcium ([Ca(2+)](i)) represent a vital signaling mechanism enabling communication between and among cells as well as with the environment. Cells have developed a sophisticated set of molecules, “the Ca(2+) toolkit,” to adapt [Ca(2+)](i) changes to specific cellular functions. Mammalian oocytes and eggs, the subject of this review, are not an exception, and in fact the initiation of embryo devolvement in all species is entirely dependent on distinct [Ca(2+)](i) responses. Here, we review the components of the Ca(2+) toolkit present in mammalian oocytes and eggs, the regulatory mechanisms that allow these cells to accumulate Ca(2+) in the endoplasmic reticulum, release it, and maintain basal and stable cytoplasmic concentrations. We also discuss electrophysiological and genetic studies that have uncovered Ca(2+) influx channels in oocytes and eggs, and we analyze evidence supporting the role of a sperm-specific phospholipase C isoform as the trigger of Ca(2+) oscillations during mammalian fertilization including its implication in fertility.

The aim of the present study was to investigate the effect of vascular endothelial growth factor (VEGF) on the meiotic and developmental competence of porcine oocytes from small follicles (SF; 0.5–3 mm diameter). When cumulus–oocyte complexes (COCs) from medium-sized follicles (MF; 3–6 mm diameter) and SF were cultured for IVM, the maturation rates were significantly higher for oocytes from MF than SF. Concentrations of VEGF in the medium were significantly higher for COCs cultured from MF than SF. When COCs from SF were exposed to 200 ng mL–1 VEGF during the first 20 h of IVM, the maturation rate improved significantly and was similar to that of oocytes derived from MF. The fertilisability of oocytes was also significantly higher than that of VEGF-free SF controls. Following parthenogenetic activation, the blastocyst formation rate improved significantly when SF COC culture was supplemented with 200 ng mL–1 VEGF, with the rate similar to that of oocytes from MF. The results of the present study indicate that VEGF markedly improves the meiotic and developmental competence of oocytes derived from SF, especially at a concentration of 200 ng mL–1 during the first 20 h of IVM.

The present study was undertaken to examine the apoptotic status and meiotic progression of oocytes from small follicle (SF; 0.5-2 mm in diameter) and medium follicle (MF; 3-6 mm in diameter) when the oocytes were denuded before, during, and after IVM. Cumulus-oocyte complexes (COCs) were collected from SF or MF of prepubertal gilt ovaries. Before or 20 hours after the start of IVM culture, some oocytes were denuded and cultured for IVM. At the end of IVM, apoptotic status and meiotic progression of the oocytes were compared with oocytes matured in the presence of cumulus cells (CCs) by Annexin-V/PI assay and 4',6-Diamidino-2-phenylindole staining. Apoptotic status of the oocytes was only affected by time when the oocytes were denuded. In both oocytes from SF and MF, although the incidence of early and late apoptotic oocytes was significantly higher when the CCs were removed before IVM, the rate was significantly lower when CCs were removed 20 and 44 hours after the start of IVM. The incidence of mature oocytes was significantly affected by both the origin of COCs and time when oocytes were denuded from the COCs. Although the percentage of mature oocytes was higher in MF than SF, maturation rates were significantly higher when oocytes were denuded 20 hours, as compared with 0 and 44 hours after the start of IVM. However, the percentage of mature oocytes with a morphologically normal spindle was significantly higher when oocytes were denuded 44 hours, rather than 22 hours of IVM. In conclusion, removing CCs 20 hours after the start of IVM seems to promote meiotic progression of the oocytes to the metaphase-II stage even when the COCs were collected from SF, although factor(s) from or communication with CCs during IVM may need to obtain a morphologically normal spindle in mature oocytes.

In mammals, fertilization initiates Ca(2+) oscillations in metaphase II oocytes, which are required for the activation of embryo development. Germinal vesicle (GV) oocytes also display Ca(2+) oscillations, although these unfold spontaneously in the absence of any known agonist(s) and their function remains unclear. We found that the main intracellular store of Ca(2+) in GV oocytes, the endoplasmic reticulum ([Ca(2+)](ER)), constitutively ‘leaks’ Ca(2+) through the type 1 inositol 1,4,5-trisphosphate receptor. The [Ca(2+)](ER) leak ceases around the resumption of meiosis, the GV breakdown (GVBD) stage, which coincides with the first noticeable accumulation of Ca(2+) in the stores. It also concurs with downregulation of the Ca(2+) influx and termination of the oscillations, which seemed underpinned by the inactivation of the putative plasma membrane Ca(2+) channels. Lastly, we demonstrate that mitochondria take up Ca(2+) during the Ca(2+) oscillations, mounting their own oscillations that stimulate the mitochondrial redox state and increase the ATP levels of GV oocytes. These distinct features of Ca(2+) homeostasis in GV oocytes are likely to underpin the acquisition of both maturation and developmental competence, as well as fulfill stage-specific cellular functions during oocyte maturation.

The fertility of sex-reversed XY female mice is severely impaired by a massive loss of oocytes and failure of meiotic progression. This phenomenon remains an outstanding mystery. We sought to determine the molecular etiology of XY oocyte dysfunction by generating sex-reversed females that bear genetic ablation of Sry, a vital sex determination gene, on an inbred C57BL/6 background. These mutant mice, termed XYsry− mutants, showed severe attrition of germ cells during fetal development, resulting in the depletion of ovarian germ cells prior to sexual maturation. Comprehensive transcriptome analyses of primordial germ cells (PGCs) and postnatal oocytes demonstrated that XYsry− females had deviated significantly from normal developmental processes during the stages of mitotic proliferation. The impaired proliferation of XYsry− PGCs was associated with aberrant β-catenin signaling and the excessive expression of transposable elements. Upon entry to the meiotic stage, XYsry− oocytes demonstrated extensive defects, including the impairment of crossover formation, the failure of primordial follicle maintenance, and no capacity for embryo development. Together, these results suggest potential molecular causes for germ cell disruption in sex-reversed female mice, thereby providing insights into disorders of sex differentiation in humans, such as “Swyer syndrome,” in which patients with an XY karyotype present as typical females and are infertile., We report the molecular etiology of XY oocyte dysfunction in sex-reversed female mice harboring Sry deletion. The results show potential molecular causes for germ cell disruption providing insights into disorders of sex differentiation in humans.

The present study was undertaken to determine the effect of a phosphodiesterase (PDE) type-5 (cyclic guanosine monophosphate-specific) inhibitor, sildenafil, on capacitation and penetration of boar spermatozoa in a basic chemically defined medium (adenosine- and theophylline-free PGM-tac4). When ejaculated spermatozoa were cultured for 90 minutes in the absence or presence of sildenafil at 2.5 mM, the inhibitor significantly increased the percentage of capacitated/acrosome-reacted spermatozoa, as a result of the chlortetracycline assay. When fresh spermatozoa were co-cultured with oocytes in the presence of sildenafil at a different concentration (0, 2.5, 25, or 250 μM), higher sildenafil concentrations (25 and 250 μM) significantly resulted in higher sperm penetration rates. When oocytes matured in vitro were co-cultured with spermatozoa in the presence of 25 μM sildenafil or 25 mM caffeine benzoate for 8 hours, the incidence of penetrated oocytes did not differ between two groups, whereas the incidence of monospermic oocytes in penetrated one was significantly higher in the presence of sildenafil. Immunocytochemical analysis reported the presence of PDE type-5 on the acrosome region of boar spermatozoa. These results report that regulation of cyclic guanosine monophosphate-specific PDE type-5 by sildenafil somehow can increase the penetrability of boar spermatozoa in vitro.

After receiving the LH surge, a mature oocyte (egg) is collected in the oviduct of mammalian females. Following fusion of the gametes, the sperm elicits in the egg repeated calcium (Ca 2 + ) transients known as oscillations, which trigger egg activation. Completion of egg activation renders the meiotic and transcriptionally silent egg into a mitotically competent, transcriptionally active zygote that eventually undergoes cell differentiation and embryo development. Here, we discuss the major events of egg activation and the molecular players that underlie them. We describe the universal role of Ca 2 + on egg activation as well as the egg's Ca 2 + toolkit. We explain how failure of egg activation results in infertility, and the value of ICSI and genetic models in identifying the molecular causes of this infertility. Finally, we point to areas where additional research is needed and how this knowledge will allow better control of fertility.

Mitochondria are abundant in fully grown mammalian oocytes with a unique spherical morphology, but the mechanisms controlling mitochondria behavior are not well understood. Here we describe for the first time the control of mitochondrial behavior in mouse oocytes by a fusion/fission mechanism. Mitofusins (Mfn1 and Mfn2) and OPA1 proteins are required for outer and inner mitochondrial membrane fusion, respectively, whereas Drp1 is the key regulator of mitochondrial fission. We show that mouse oocytes express the Mfn1, Mfn2, Opa1 and Drp1 proteins, both in immature and mature oocytes at similar levels. Overexpression of Mfn1 or Mfn2 causes marked mitochondrial aggregation, particularly in the perinuclear region during meiotic progression. Tracking of mitochondria with chromosomes or endoplasmic reticulum (ER) throughout oocyte maturation demonstrates that Mfn1 and Mfn2-promoted mitochondrial aggregation disturbs the spatiotemporal dynamic of the chromosomes and ER, respectively. Our findings suggest that organelle dynamics are co-ordinately controlled during meiotic division, and an imbalance of mitochondrial fusion/fission leads to disorganization of the organelle compartments.

Changes in the intracellular concentration of calcium ([Ca2+]i) represent a vital signaling mechanism enabling communication between and among cells as well as with the environment. Cells have developed a sophisticated set of molecules, "the Ca2+ toolkit," to adapt [Ca2+]i changes to specific cellular functions. Mammalian oocytes and eggs, the subject of this review, are not an exception, and in fact the initiation of embryo devolvement in all species is entirely dependent on distinct [Ca2+]i responses. Here, we review the components of the Ca2+ toolkit present in mammalian oocytes and eggs, the regulatory mechanisms that allow these cells to accumulate Ca2+ in the endoplasmic reticulum, release it, and maintain basal and stable cytoplasmic concentrations. We also discuss electrophysiological and genetic studies that have uncovered Ca2+ influx channels in oocytes and eggs, and we analyze evidence supporting the role of a sperm-specific phospholipase C isoform as the trigger of Ca2+ oscillations during mammalian fertilization including its implication in fertility.

Global transcriptome studies have provided important information advancing our understanding of nuclear reprogramming in somatic cell nuclear transfer (SCNT) embryos. The expression of the Eif1a gene is down-regulated in mouse Sertoli cell nuclear transfer (SeCNT) embryos during the preimplantation stages, however its protein expression level remains unclear. Here we observed the protein expression level of EIF1A by immunofluorescence and western blot analysis during the preimplantation stages in mouse SeCNT embryos. The results reveal that EIF1A protein is constantly expressed in germinal-vesicle and metaphase II oocytes and preimplantation stage embryos. Importantly, the localization and expression level of EIF1A were similar in control in vitro fertilized embryos and SeCNT embryos. Thus, since maternally derived EIF1A persisted throughout preimplantation development, repression of Eif1a is not likely to be involved in the developmental potency of mouse SeCNT embryos.

The objective of this study was to compare the cAMP and cGMP levels in cumulus-oocyte complexes (COCs) derived from the middle follicles (MFs, 3-6 mm in diameter) and small follicles (SFs, 1-3 mm in diameter) of pre-pubertal gilts during the first 24-h period of maturation in vitro (IVM). Both cAMP and cGMP levels in MF- and SF-derived oocytes did not change during this period. Although the cAMP levels increased in the COCs at 10 and 20 h after the start of IVM, the levels of cAMP were significantly higher in MF-derived COCs than in SF-derived COCs at 20 h after the start of IVM. On the other hand, the cGMP levels in COCs decreased to basal levels between 10 and 20 h after the start of the IVM, whereas cGMP levels were lower in SF-derived COCs than in MF-derived COCs during the first 10 h. The number of cumulus cells was larger in the MF-derived COCs than in the SF-derived COCs during the first 20-h period of IVM. The estimated cAMP level per cumulus cell at 10 h after the start of the IVM was higher in SF-derived COCs than in MF-derived COCs, whereas the estimated cGMP level per cumulus cell was no different between MF- and SF-derived COCs. From these results, we conclude that cAMP and cGMP levels in COCs, but not in oocytes, drastically change during the first 20-h period of IVM, and that both cAMP and cGMP levels significantly differ between MF- and SF-derived COCs.

A sperm-specific phospholipase C (PLC), PLCzeta (PLCζ), is thought to underlie the initiation of calcium ([Ca(2+) ]i ) oscillations that induce egg activation in mammals. In large domestic species, only bovine, porcine and recently equine PLCζ have been cloned, and the physiological functions of these molecules have not been fully characterized. Here, we evaluated the physiological functions of equine PLCζ (ePLCζ) in mouse oocytes. ePLCζ was cloned from testis using RT-PCR. The expression of ePLCζ messenger RNA was confirmed in testis but not in other tissues. Microinjection of ePLCζ complementary RNA (cRNA) into mouse oocytes induced long-lasting [Ca(2+) ]i oscillations, and most of the injected oocytes formed pronuclei (PN). The injection of cRNAs encoding horse, mouse, human and cow PLCζ into mouse oocytes showed that ePLCζ had the highest [Ca(2+) ]i oscillation-inducing activity among the species tested. Mutation of D202R, which renders the protein inactive, abrogated the activity of ePLCζ. The nuclear translocation ability of ePLCζ was defective when expressed in mouse oocytes. Taken together, our findings show for the first time that ePLCζ has highest activity of the mammalian species studied to date. Our findings will be useful for the improvement of reproductive technologies in the horse.

The activation of the developmental program in mammalian eggs relies on the initiation at the time of fertilization of repeated rises in the intracellular concentration of free calcium ([Ca(2+)](i)), also known as [Ca(2+)](i) oscillations. The ability to mount the full complement of oscillations is only achieved at the end of oocyte maturation, at the metaphase stage of meiosis II (MII). Over the last decades research has focused on addressing the mechanisms by which the sperm initiates the oscillations and identification of the channels that mediate intracellular Ca(2+) release. This review will describe the up-to-date knowledge of other aspects of Ca(2+) homeostasis in mouse oocytes, such as the mechanisms that transport Ca(2+) out of the cytosol into the endoplasmic reticulum (ER), the Ca(2+) store of the oocyte/egg, into other organelles and also those that extrude Ca(2+). Evidence pointing to channels in the plasma membrane that mediate Ca(2+) entry from the extracellular milieu, which is required for the persistence of the oscillations, is also discussed, along with the modifications that these mechanisms undergo during maturation. Lastly, we highlight areas where additional research is needed to obtain a better understating of the molecules and mechanisms that regulate Ca(2+) homeostasis in this unique Ca(2+) signaling system.

Changes in Ca2+ homeostasis render oocytes competent to undergo [Ca2+]i oscillations and activation. During mouse oocyte maturation Ca2+ influx and SOCE are down-regulated, whereas [Ca2+]ER content increases. Bypassing the down-regulation of Ca2+ influx disturbs oocyte maturation., In preparation for fertilization, mammalian oocytes undergo optimization of the mechanisms that regulate calcium homeostasis. Among these changes is the increase in the content of the Ca2+ stores ([Ca2+]ER), a process that requires Ca2+ influx. Nevertheless, the mechanism(s) that mediates this influx remains obscure, although is known that [Ca2+]ER can regulate Ca2+ influx via store-operated Ca2+ entry (SOCE). We find that during maturation, as [Ca2+]ER increases, Ca2+ influx decreases. We demonstrate that mouse oocytes/eggs express the two molecular components of SOCE—stromal interaction molecule 1 (Stim1) and Orai1—and expression of human (h) Stim1 increases Ca2+ influx in a manner that recapitulates endogenous SOCE. We observe that the cellular distribution of hStim1 and hOrai1 during maturation undergoes sweeping changes that curtail their colocalization during the later stages of maturation. Coexpression of hStim1 and hOrai1 enhances influx throughout maturation but increases basal Ca2+ levels only in GV oocytes. Further, expression of a constitutive active form of hStim1 plus Orai1, which increases basal Ca2+ throughout maturation, disturbs resumption of meiosis. Taken together, our results demonstrate that Ca2+ influx and SOCE are regulated during maturation and that alteration of Ca2+ homeostasis undermines maturation in mouse oocytes.

The germ line reprogramming barrier resets parental epigenetic modifications according to sex, conferring totipotency to mammalian embryos upon fertilization. However, it is not known whether epigenetic errors are committed during germ line reprogramming that are then transmitted to germ cells, and consequently to offspring. We addressed this question in the present study by performing a genome-wide DNA methylation analysis using a target postbisulfite sequencing method in order to identify DNA methylation errors in cloned mouse sperm. The sperm genomes of two somatic cell-cloned mice (CL1 and CL7) contained significantly higher numbers of differentially methylated CpG sites (P = 0.0045 and P = 0.0116). As a result, they had higher numbers of differentially methylated CpG islands. However, there was no evidence that these sites were transmitted to the sperm genome of offspring. These results suggest that DNA methylation errors resulting from embryo cloning are transmitted to the sperm genome by evading the germ line reprogramming barrier.

Intracellular distribution of mitochondria varies during development of the oocyte into a fertilizable egg. Here we demonstrate a change in the distribution of mitochondria during oocyte growth and maturation in living mouse oocytes. In growing oocytes, mitochondria concentrated into subcortical and perinuclear areas, whereas it diffusely distributed throughout the cytoplasm in fully-grown oocytes, indicating the variation of mitochondrial distribution in the same G2/M cell-cycle stages. GFP-labeled mitochondria reveal that oocyte maturation involves dynamic reorganization of the mitochondria, and whose process is associated with microtubule organization. These spatio-temporal regulations of mitochondria in oocytes may be important process in the preparation of fertilization and subsequent embryonic development.

At the time of fertilization, an increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) underlies egg activation and initiation of development in all species studied to date. The inositol 1,4,5-trisphosphate receptor (IP(3)R1), which is mostly located in the endoplasmic reticulum (ER) mediates the majority of this Ca(2+) release. The sensitivity of IP(3)R1, that is, its Ca(2+) releasing capability, is increased during oocyte maturation so that the optimum [Ca(2+)](i) response concurs with fertilization, which in mammals occurs at metaphase of second meiosis. Multiple IP(3)R1 modifications affect its sensitivity, including phosphorylation, sub-cellular localization, and ER Ca(2+) concentration ([Ca(2+)](ER)). Here, we evaluated using mouse oocytes how each of these factors affected IP(3)R1 sensitivity. The capacity for IP(3)-induced Ca(2+) release markedly increased at the germinal vesicle breakdown stage, although oocytes only acquire the ability to initiate fertilization-like oscillations at later stages of maturation. The increase in IP(3)R1 sensitivity was underpinned by an increase in [Ca(2+)](ER) and receptor phosphorylation(s) but not by changes in IP(3)R1 cellular distribution, as inhibition of the former factors reduced Ca(2+) release, whereas inhibition of the latter had no impact. Therefore, the results suggest that the regulation of [Ca(2+)](ER) and IP(3)R1 phosphorylation during maturation enhance IP(3)R1 sensitivity rendering oocytes competent to initiate oscillations at the expected time of fertilization. The temporal discrepancy between the initiation of changes in IP(3)R1 sensitivity and acquisition of mature oscillatory capacity suggest that other mechanisms that regulate Ca(2+) homeostasis also shape the pattern of oscillations in mammalian eggs.

The developmental competence of mammalian eggs is compromised by postovulatory aging. We and others have found that in these eggs, the intracellular calcium ([Ca(2+)](i)) responses required for egg activation and initiation of development are altered. Nevertheless, the mechanism(s) underlying this defective Ca(2+) release is not well known. Here, we investigated if the function of IP(3)R1, the major Ca(2+) release channel at fertilization, was undermined in in vitro-aged mouse eggs. We found that in aged eggs, IP(3)R1 displayed reduced function as many of the changes acquired during maturation that enhance IP(3)R1 Ca(2+) conductivity, such as phosphorylation, receptor reorganization and increased Ca(2+) store content ([Ca(2+)](ER)), were lost with increasing postovulatory time. IP(3)R1 fragmentation, possibly associated with the activation of caspase-3, was also observed in these eggs. Many of these changes were prevented when the postovulatory aging of eggs was carried out in the presence of caffeine, which minimized the decline in IP(3)R(1) function and maintained [Ca(2+)](ER) content. Caffeine also maintained mitochondrial membrane potential, as measured by JC-1 fluorescence. We therefore conclude that [Ca(2+)](i) responses in aged eggs are undermined by reduced IP(3)R1 sensitivity, decreased [Ca(2+)](ER) , and compromised mitochondrial function, and that addition of caffeine ameliorates most of these aging-associated changes. Understanding the molecular basis of the protective effects of caffeine will be useful in elucidating, and possibly reversing, the signaling pathway(s) compromised by in vitro culture of eggs.

Oxygen consumption reflects overall metabolic activity of mammalian embryos. We measured oxygen consumption in individual porcine somatic cell nuclear transfer (SCNT) and in vitro-fertilized (IVF) embryos by modified scanning electrochemical microscopy. Oxygen consumption in IVF embryos rapidly increased at day 5 of the blastocyst stage (D5BL). IVF embryos that consumed0.81 x 10(14)/mol sec(-1) of oxygen at D5BL exhibited significantly higher hatching and hatched rates at D7BL, whereas D5BL SCNT embryos using porcine fetal fibroblasts did not show an increase in oxygen consumption until D7BL. The numbers of inner cell mass and trophectoderm (TE) cells and incidence of apoptosis did not significantly differ between IVF and SCNT embryos at D5BL. At D7BL, a significant lower number of TE cell and higher incidence of apoptosis were observed in SCNT than in IVF embryos; this significantly correlated with their oxygen consumption at D5BL. Use of cumulus cells as donor cells neutralized the low oxygen consumption in SCNT embryos at D5BL, regardless of the difference between the recipient cytoplasm and donor nucleus. Some of SCNT embryos at D7BL were retrieved the hatching completion and were improved the number of TE cell and apoptosis incidence by using cumulus cells. Thus, anomalous oxygen consumption in porcine SCNT embryos at D5BL could be sign of limited hatchability, which may be responsible for the low TE cell number and high apoptosis incidence.

We investigated the effects of in vitro maturation duration and treatment with dibutyryl cyclic adenosine monophosphate (dbcAMP) on the blind enucleation efficiency and developmental competence of miniature pig somatic cell nuclear transfer (SCNT) embryos. Oocytes were cultured for 22 h in NCSU-23 medium with or without 1 mM dbcAMP and then additionally cultured in dbcAMP-free NCSU-23 for 14, 18, or 22 h. Regardless of dbcAMP treatment, the rate of nuclear maturation reached a plateau at 36 and 40 h. However, mitochondrial distribution, a marker for cytoplasmic maturation, differed between the dbcAMP-untreated oocytes at 36 h and dbcAMP-treated oocytes at 40 h. The metaphase II chromosomes were adjacent to the first polar body in 68.8% and 63.5% of the dbcAMP-untreated oocytes at 36 h and dbcAMP-treated oocytes at 40 h, respectively. Furthermore, the blind enucleation efficiency by removing a small volume of cytoplasm was significantly higher in the dbcAMP-untreated oocytes at 36 h (82.9%) and dbcAMP-treated oocytes at 40 h (89.9%) than other groups. The rate of blastocyst formation was highest in the dbcAMP-treated oocytes at 40 h. Hence, this study demonstrated that dbcAMP-treated early metaphase II oocytes are suitable for the production of miniature pig SCNT embryos.

Successful cloning by somatic cell nuclear transfer (SCNT) requires a reprogramming process in which the epigenetic state of a differentiated donor nucleus must be converted into an embryonic totipotent state. However, this epigenetic reprogramming is incomplete in SCNT embryos, causing low production efficiency. Recently, it has been reported that trichostatin A (TSA), an inhibitor of histone deacetylase, potentially enhances cloning efficiency. The aim of the present study was to optimize the TSA treatment for miniature pig SCNT embryos and investigate the effect of the acetylation level of histone on developmental competence of SCNT embryos. In order to optimize the TSA treatment, we examined the developmental competence of SCNT embryos under various exposure times (0-50 h) and concentrations (0-500 nM). Treatment with 5 nM TSA for 15 and 20 h beginning at the start of activation significantly increased the blastocyst formation rate (34.6 and 32.4 vs. 18.2%, respectively) and mean cell number (57.0 +/- 2.7 and 56.6 +/- 2.7 vs. 43.5 +/- 2.1, respectively) as compared with the non-treated group (0 h). We then investigated the acetylation levels of histone H3 in SCNT embryos treated with or without TSA (TSA (+) or TSA (-)) as compared with in vitro- fertilized (IVF) embryos. The acetylation levels of the TSA (-) SCNT embryos at the pseudo-pronuclear and 2-cell stages were significantly lower than those of the IVF embryos at the same developmental stages. In contrast, the acetylation levels of the TSA (+) SCNT embryos were similar to those of the IVF embryos. There was no difference in the acetylation levels of all groups at the blastocyst stage. Our data therefore suggests that the acetylation level of histone H3 at the pseudo-pronuclear and 2-cell stages is positively correlated with subsequent development of SCNT embryos, which may be an important event for the vital development of SCNT embryos in miniature pigs.

We evaluated the developmental competence of somatic cell nuclear transfer (SCNT) embryos using in vitro embryo culture systems. Embryos were cultured in NCSU-23, NCSU-23 supplemented with essential and non-essential amino acids (NCSU-23aa) or modified PZM-5 supplemented with BSA instead of PVA (mPZM-5). The rates of blastocyst formation were significantly higher in the mPZM-5 group than in the other groups, regardless of the method of embryo production (38.0 vs. 25.3 or 29.1% for IVF, 18.2 vs. 8.7 or 9.4% for SCNT, respectively). The mean cell numbers of IVF and SCNT blastocysts were also significantly higher in mPZM-5 than in the other groups (62.0 vs. 42.3 or 43.0 for IVF, 46.5 vs. 29.4 or 31.3 for SCNT, respectively). Next, the embryos were cultured in mPZM-5 from days 0 to 4 and then in mPZM-5 (P/P), NCSU-23 (P/N) or NCSU-23aa (P/Naa) until day 6. The rates of blastocyst formation were similar among the 3 two-step culture systems in both embryo groups (36.2, 34.2, and 33.6% for IVF, 20.8, 14.1, and 17.2% for SCNT, respectively). The mean cell number in the IVF and SCNT blastocysts was significantly lower in P/N than in P/ P and P/Naa (46.5 vs. 63.5 and 68.7 for IVF, 29.3 vs. 45.5 and 39.7 for SCNT, respectively). Next, we examined the effect of media on apoptosis in IVF and SCNT blastocysts. The apoptosis indices in the blastocysts derived from either NCSU- 23 or mPZM-5 were analyzed by TUNEL assay. The apoptosis index of the SCNT blastocysts was significantly lower in mPZM-5 than in NCSU-23 (8.8 vs. 13.6%), whereas no such difference was observed between groups in the IVF embryos (5.1 vs. 4.4%). These data suggested that SCNT embryos were more easily affected by culture environment compared with IVF embryos, offering the possibility to further enhance the developmental competence of SCNT embryos by developing more appropriate culture conditions in pigs.

The germ line reprogramming barrier resets parental epigenetic modifications according to sex, conferring totipotency to mammalian embryos upon fertilization. However, it is not known whether epigenetic errors are committed during germ line reprogramming that are then transmitted to germ cells, and consequently to offspring. We addressed this question in the present study by performing a genome-wide DNA methylation analysis using a target postbisulfite sequencing method in order to identify DNA methylation errors in cloned mouse sperm. The sperm genomes of two somatic cell-cloned mice (CL1 and CL7) contained significantly higher numbers of differentially methylated CpG sites (P = 0.0045 and P = 0.0116). As a result, they had higher numbers of differentially methylated CpG islands. However, there was no evidence that these sites were transmitted to the sperm genome of offspring. These results suggest that DNA methylation errors resulting from embryo cloning are transmitted to the sperm genome by evading the germ line reprogramming barrier.

In mammalian ovary, follicular development in mammals is regulated by the complex process including endocrine, paracrine and autocrine. During the last decade, the role of growth factors in ovarian folliculogenesis has been extensively studied in mammals. In particular, a growing body of evidence indicates that the vascular endothelial growth factor (VEGF) system plays a key role in follicular development and atresia in the woman, rodents and domestic animal species. More recently, the bone morphogenetic protein (BMP) and growth differentiation factor (GDF) that belong to TGF-beta family have been shown to be involved in the regulation of follicle growth. In this paper, we will essentially consider the role of these growth factor systems in mammalian ovary. Moreover, we will review recent patents associated with ovarian follicular development in mammals.

When the nucleus in G0/G1 phase is transferred to an enucleated oocyte by nuclear transfer (NT), its nuclear envelope is broken, followed by condensation of chromosome structure by maturation promoting factor (MPF). This morphological remodeling of the transferred interphase nucleus seems to be essential for subsequent development of NT embryos. In this study, we treated porcine NT embryos with caffeine, which has been reported to increase MPF activity, to keep their MPF level high during NT. When 2.5 mM caffeine was added to the handling medium, the proportion of NT embryos showing condensed chromosome increased significantly (P < 0.05). In NT embryos treated with caffeine, the activity of p34cdc2 kinase was significantly (P < 0.05) higher than in those without caffeine at 3 h post-injection. In addition, the rate of development to the blastocyst stage after activation was significantly (P < 0.05) higher in NT embryos treated with caffeine. These results indicate that caffeine treatment can increase not only the rate of chromosome condensation but also the developmental rate to the blastocyst stage of porcine NT embryos. This action is most likely due to the support/increase of MPF activity throughout the process of NT.

A decline in fertility occurs with age. Because the extracellular matrix has a vital role in maintaining the integrity and determining the tissue function of numerous organs, the reasons for this fertility reduction may be associated with changes occurring in the ovarian matrix. To demonstrate this hypothesis, by using Picrosirius Red (PSR), a connective tissue dye specific for fibres of collagen I and III, we examined the ovarian tunica albuginea (TA), a part of the cortex composed by dense connective tissue that protects the ovaries and whose rupture is critical for the occurrence of ovulation events. According to an approval from the Ethics Committee of Okayama University (approval number 1818), ovaries were obtained from patients with gender identity disorder at the Okayama University Hospital. Sliced ovaries were fixed in 4% paraformaldehyde and included in paraffin. Sections of 5 μm thickness were stained with PSR. For each individual, 2 non-overlapping brightfield images were taken of each section with a fluorescence microscope and the attached viewer software (Keyence BZ-X710, Keyence Corp., Osaka, Japan). ImageJ (National Institutes of Health, Bethesda, MD, USA) was used to quantify the distance of the dense connective tissue by selecting 5 random points manually per image and, to quantify the density of the tissue; we detected PSR staining above a determined threshold kept constant for all the images analysed. Statistical analyses of data from 3 replicates per individual were performed by Pearson’s correlation, and a P-value

In mammals, genomic imprinting governed by DNA methyltransferase DNMT3A and its cofactor DNMT3L is essential for functional gametes. Oocyte-specific methylation imprints are established during oocyte growth concomitant with DNMT3A/DNMT3L expression, although the mechanisms of oocyte-specific imprinting are not fully understood. To determine whether the presence of DNMT3A/DNMT3L in oocytes is sufficient for acquisition of methylation imprints, we produced transgenic mice to induce DNMT3A/DNMT3L expression prematurely in oogenesis and analyzed DNA methylation imprints. The results showed that 2- to 4-fold greater expression of DNMT3A/DNMT3L was achieved in non-growing (ng) oocytes versus fully grown oocytes derived from wild-type mice, but the analyzed imprint domains were not methylated. Thus, the presence of DNMT3A/DNMT3L in ng oocytes is insufficient for methylation imprints, and imprinted regions are resistant to DNMT3A/DNMT3L in ng oocytes. In contrast, excess DNMT3A/DNMT3L accelerated imprint acquisition at Igf2r, Lit1, Zac1 and Impact but not Snrpn and Mest in growing oocytes. Therefore, DNMT3A/DNMT3L quantity is an important factor for imprint acquisition. Transcription at imprinted domains is proposed to be involved in de novo methylation; however, transcription at Lit1, Snrpn and Impact was observed in ng oocytes. Thus, transcription cannot induce DNMT3A catalysis at imprinted regions even if DNMT3A/DNMT3L is present. However, the accelerated methylation imprints in oocytes, with the exception of Igf2r, were erased during embryogenesis. In conclusion, a sufficient amount of DNMT3A/DNMT3L and a shift from the resistant to permissive state are essential to establish oocyte-specific methylation imprints and that maintenance of the acquired DNA methylation imprints is essential for functional imprinting.

Since the birth of the first cloned sheep, “Dolly”, many studies have reported the successful use of cloning by somatic cell nuclear transfer in other mammalian species. In spite of these successes, the efficiency of this technique is low, with less than 10% of generated embryos resulting in offspring. Factors of genetic, epigenetic, and technical origin seem to affect the efficiency of cloning. Further, because these reconstructed embryos do not have the benefit of being activated by the sperm, egg activation relies on artificial procedures such as those delivered by chemical or physical stimuli. In general, these stimuli aim to replicate either the signal delivered by the sperm, namely, elevations in the intracellular concentration of calcium ion ([Ca2+]i), or the outcome of this signal, inactivation of the M-phase kinases that are responsible for the metaphase II arrest. In mammalian fertilization, the sperm initiates repetitive increases in [Ca2+]i that are also known as oscillations, and experimentally replicating these oscillations has been difficult to accomplish, except in mouse eggs where oscillations can be attained by replacing extracellular CaCl2 with SrCl2. In other mammalian species, in the absence of oscillations, most activation protocols incorporate chemical methods to subdue the activity of the M-phase kinases. Here, we will briefly describe oocyte activation protocols presently in use in different species, highlight some of their advantages and disadvantages, and discuss possible improvements.

Recent studies of the demethylation process in murine zygotes have shown that 5-methylcytosine (5mC) is first converted into 5-hydroxymethylcytosine (5hmC) or further-oxidized cytosines in the paternal genome by the maternal ten–eleven translocation 3 (TET3) enzyme. This process is crucial for normal embryogenesis, and our aim was to elucidate the effect of Tet3 on the maternal genome during female germ-line development. Immunofluorescence analysis showed that 5hmC was clearly present in fully grown oocytes but not in nongrowing and early growth-stage oocytes. The 5hmC in the maternal genome was clearly detectable in DNA methyltransferase 3-like enzyme (Dnmt3L)-null oocytes and their fertilized zygotes, although Dnmt3L is essential for DNA methylation in oocytes. An analysis using an enzyme digestion-based method showed that 5hmC was present in LTR retrotransposons from the late growth period of oocytes. Quantitative RT-PCR analysis showed that Tet3 expression was enhanced during oocyte growth and exhibited an approximately 40-fold increase between nongrowing and fully grown oocytes. Our results show that 5hmC is generated since the oocyte growth stage, accompanied by up-regulation of Tet3; 5hmC is located mainly in LTR retrotransposons, indicating that 5hmC generated in growth-stage oocytes is responsible for genomewide demethylation after fertilization.

DNA methylation imprints that are established in spermatogenesis and oogenesis are essential for functional gametes. However, the mechanisms underlying gamete-specific imprinting remain unclear. In this study, we investigated whether male and female gametes derived from newborn mice are epigenetically plastic and whether DNA methylation imprints are influenced by the niche surrounding the nuclei of the gametes. When prospermatogonia possessing sperm-specific DNA methylation imprints were fused with enucleated fully grown oocytes and exposed to the ooplasm for 5–6 days, the DNA methylation status of the reconstituted oocytes remained identical to that of prospermatogonia for all the imprinted regions analysed. These results suggest that the imprinting status of prospermatogonia is stable and that the epigenome of prospermatogonia loses sexual plasticity. By contrast, when non-growing oocytes lacking oocyte-specific DNA methylation imprints were fused with enucleated fully grown oocytes and the reconstituted oocytes were then cultured for 5–6 days, theIgf2r,Kcnq1ot1and, unexpectedly,H19/Igf2differentially methylated regions (DMRs) were methylated. Methylation imprints were entirely absent in oocytes derived from 5-day-old mice, andH19/Igf2DMR is usually methylated only in spermatogenesis. These findings indicate that in the nuclei of non-growing oocytes the chromatin conformation changes and becomes permissive to DNA methyltransferases in some DMRs and that mechanisms for maintaining non-methylated status at theH19/Igf2DMR are lost upon long exposure to mature ooplasm.

Changes in the intracellular concentration of free calcium ([Ca2+]i) regulate diverse cellular processes including fertilization. In mammalian eggs, the [Ca2+]i changes induced by the sperm unfold in a pattern of periodical rises, also known as [Ca2+]i oscillations. The source of Ca2+ during oscillations is the endoplasmic reticulum ([Ca2+]ER), but it is presently unknown how [Ca2+]ER is regulated. Here, we show using mouse eggs that [Ca2+]i oscillations induced by a variety of agonists, including PLCζ, SrCl2 and thimerosal, provoke simultaneous but opposite changes in [Ca2+]ER and cause differential effects on the refilling and overall load of [Ca2+]ER. We also found that Ca2+ influx is required to refill [Ca2+]ER, because the loss of [Ca2+]ER was accelerated in medium devoid of Ca2+. Pharmacological inactivation of the function of the mitochondria and of the Ca2+-ATPase pumps PMCA and SERCA altered the pattern of oscillations and abruptly reduced [Ca2+]ER, especially after inactivation of mitochondria and SERCA functions. We also examined the expression of SERCA2b protein and found that it was expressed throughout oocyte maturation and attained a conspicuous cortical cluster organization in mature eggs. We show that its overexpression reduces the duration of inositol-1,4,5-trisphosphate-induced [Ca2+]i rises, promotes initiation of oscillations and enhances refilling of [Ca2+]ER. Collectively, our results provide novel insights on the regulation of [Ca2+]ER oscillations, which underlie the unique Ca2+-signalling system that activates the developmental program in mammalian eggs. ispartof: Journal of Cell Science vol:126 issue:24 pages:5714-5724 ispartof: location:England status: published

Dynamic epigenetic reprogramming occurs during mammalian germ cell development, although the targets of this process, including DNA demethylation and de novo methylation, remain poorly understood. We performed genome-wide DNA methylation analysis in male and female mouse primordial germ cells at embryonic days 10.5, 13.5, and 16.5 by whole-genome shotgun bisulfite sequencing. Our high-resolution DNA methylome maps demonstrated gender-specific differences in CpG methylation at genome-wide and gene-specific levels during fetal germline progression. There was extensive intra- and intergenic hypomethylation with erasure of methylation marks at imprinted, X-linked, or germline-specific genes during gonadal sex determination and partial methylation at particular retrotransposons. Following global demethylation and sex determination, CpG sites switched to de novo methylation in males, but the X-linked genes appeared resistant to the wave of de novo methylation. Significant differential methylation at a subset of imprinted loci was identified in both genders, and non-CpG methylation occurred only in male gonocytes. Our data establish the basis for future studies on the role of epigenetic modifications in germline development and other biological processes.

This experiment was undertaken to assess the meiotic and developmental competences of oocytes derived from different sized follicles and denuded of cumulus cells 0, 20, and 44 h after the start of culture for in vitro maturation (IVM). Groups of 60 oocyte-cumulus complexes from small- (SF

Background Dynamic epigenetic reprogramming occurs during mammalian germ cell development, whereas the targets of this process including DNA demethylation and de novo methylation remain poorly understood. Here, we examined genome-wide methylation profiles in developing primordial germ cells (PGCs) of mice using high-throughput shotgun sequencing of bisulfite-treated DNA (whole-genome shotgun bisulfite sequencing; WGSBS), which accurately quantifies whole-genome methylation levels at single-base resolution.

A sperm-specific phospholipase C (PLC), PLCzeta (PLCζ), is thought to underlie the initiation of calcium ([Ca(2+) ]i ) oscillations that induce egg activation in mammals. In large domestic species, only bovine, porcine and recently equine PLCζ have been cloned, and the physiological functions of these molecules have not been fully characterized. Here, we evaluated the physiological functions of equine PLCζ (ePLCζ) in mouse oocytes. ePLCζ was cloned from testis using RT-PCR. The expression of ePLCζ messenger RNA was confirmed in testis but not in other tissues. Microinjection of ePLCζ complementary RNA (cRNA) into mouse oocytes induced long-lasting [Ca(2+) ]i oscillations, and most of the injected oocytes formed pronuclei (PN). The injection of cRNAs encoding horse, mouse, human and cow PLCζ into mouse oocytes showed that ePLCζ had the highest [Ca(2+) ]i oscillation-inducing activity among the species tested. Mutation of D202R, which renders the protein inactive, abrogated the activity of ePLCζ. The nuclear translocation ability of ePLCζ was defective when expressed in mouse oocytes. Taken together, our findings show for the first time that ePLCζ has highest activity of the mammalian species studied to date. Our findings will be useful for the improvement of reproductive technologies in the horse.

During fertilization in mammalian species, a sperm-induced intracellular Ca(2+) signal ([Ca(2+)](i)) mediates both exit of meiosis and oocyte activation. Recently, we demonstrated in mouse oocytes that the phosphorylation levels of inositol 1,4,5 trisphosphate receptor type1 (IP(3)R1), the channel responsible for Ca(2+) release and oscillations during fertilization, changed during maturation and fertilization. Therefore, we examined the expression and phosphorylation of IP(3)R1 during in vitro maturation of pig oocytes. Here, our present study shows that expression of IP(3)R1 protein did not change during maturation, although the phosphorylation status of the receptor, specifically at an MPM-2 epitope, did. We found that while at the beginning of maturation IP(3)R1 lacked MPM-2 immunoreactivity, it became MPM-2 reactive by 24 h and reached maximal reactivity by 36 h. Interestingly, the acquisition of MPM-2 reactivity coincided with the activation of p34(cdc2) kinase and mitogen-activated protein kinase (MAPK), which are involved in meiotic progression. Following completion of maturation, inactivation of MAPK by U0126 did not affect IP(3)R1 phosphorylation, although inactivation of p34(cdc2) kinase by roscovitine dramatically reduced IP(3)R1 phosphorylation. Neither inhibitor affected total expression of IP(3)R1. Altogether, our results show that IP(3)R1 undergoes dynamic phosphorylation during maturation and this might underlie the generation of oscillations at fertilization. ispartof: Animal Science Journal vol:81 issue:1 pages:34-41 ispartof: location:Australia status: published

Egg activation and further embryo development require a sperm-induced intracellular Ca(2+) signal at the time of fertilization. Prior to fertilization, the egg's Ca(2+) machinery is therefore optimized. To this end, during oocyte maturation, the sensitivity, i.e. the Ca(2+) releasing ability, of the inositol 1,4,5-trisphosphate receptor type 1 (IP(3)R1), which is responsible for most of this Ca(2+) release, markedly increases. In this study, the recently discovered specific Polo-like kinase (Plk) inhibitor BI2536 was used to investigate the role of Plk1 in this process. BI2536 inactivates Plk1 in oocytes at the early stages of maturation and significantly decreases IP(3)R1 phosphorylation at an MPM-2 epitope at this stage. Moreover, this decrease in Plk1-dependent MPM-2 phosphorylation significantly lowers IP(3)R1 sensitivity. Finally, using in vitro phosphorylation techniques we identified T(2656) as a major Plk1 site on IP(3)R1. We therefore propose that the initial increase in IP(3)R1 sensitivity during oocyte maturation is underpinned by IP(3)R1 phosphorylation at an MPM-2 epitope(s). ispartof: CELL CALCIUM vol:46 issue:1 pages:56-64 ispartof: location:Netherlands status: published

In mammalian ovary, follicular development in mammals is regulated by the complex process including endocrine, paracrine and autocrine. During the last decade, the role of growth factors in ovarian folliculogenesis has been extensively studied in mammals. In particular, a growing body of evidence indicates that the vascular endothelial growth factor (VEGF) system plays a key role in follicular development and atresia in the woman, rodents and domestic animal species. More recently, the bone morphogenetic protein (BMP) and growth differentiation factor (GDF) that belong to TGF-beta family have been shown to be involved in the regulation of follicle growth. In this paper, we will essentially consider the role of these growth factor systems in mammalian ovary. Moreover, we will review recent patents associated with ovarian follicular development in mammals.

SummaryIn many animals, cytochalasins have generally been used as cytoskeletal inhibitors for the diploid complement retention of somatic cell nuclear transfer (SCNT) embryos. However, limited information is available on the effects of cytochalasins on the in vitro development of SCNT embryos. Hence, we compared the effects of cytochalasin B (CB) and cytochalasin D (CD) on pseudo-polar body (pPB) extrusion, cortical actin filament (F-actin) distribution in porcine parthenogenetic oocytes and in vitro development of SCNT embryos that were reconstructed using foetal fibroblasts in the G0/G1 phase derived from miniature pigs. CB (7.5 μg/ml) and CD (2.5 μg/ml) treatments effectively inhibited pPB extrusion in SCNT embryos. CB (2.5 μg/ml) treatment could not inhibit pPB extrusion and insufficiently destabilized F-actin immediately following artificial activation. In parthenogenetic oocytes treated with 2.5 μg/ml CD, normal reorganization and uniform distribution of cortical F-actin at the cytoplasmic membrane were observed at 8 h after artificial activation; this finding was similar to that of control oocytes. In contrast, parthenogenetic oocytes treated with 7.5 μg/ml CB showed non-uniform distribution of F-actin at 8 h after artificial activation. On day 5 after in vitro cultivation, the blastocyst formation rate of SCNT embryos treated with 2.5 μg/ml CD was significantly higher than that of SCNT embryos treated with 2.5 and 7.5 μg/ml CB (p < 0.05). Hence, the present findings suggest that CD is more effective than CB as the cytoskeletal inhibitor for the production of SCNT embryos in miniature pigs.

For production of viable somatic cell nuclear transferred (SCNT) miniature pig embryos, in vitro condition for controlling the quality of recipient oocytes derived from domestic pig ovaries should be evaluated. In the present study, to get information on optimal in vitro maturation (IVM) condition of oocytes, we investigated the effect of IVM duration of recipient oocytes on subsequent development of SCNT miniature pig embryos, the maturation-promoting factor (MPF) activity in recipient oocytes before and after SCNT, and the occurrence of premature chromosome condensation (PCC) and spindle morphologies of donor nuclei following SCNT. The optimal window of the IVM period in terms of in vitro developmental ability of SCNT embryos was determined to be 36-40 h after the start of IVM. The use of recipient oocytes matured for 36 and 40 h resulted in a high level of MPF activity before and after SCNT, and increased the occurrence of PCC in transferred nuclei compared to the use of oocytes matured for 44 and 52 h. The proportion of abnormal spindle-like structures increased as the IVM period was prolonged. In addition, SCNT embryos constructed from recipient cytoplasts obtained after 40 h of maturation by using fetal fibroblasts of miniature pigs were transferred to surrogate miniature pigs, and developed to full term. These results suggest that recipient oocytes matured for 36 h and 40 h effectively induce PCC with a normal cytoskeletal structure because of a high level of MPF activity; furthermore, the 40-h IVM period improves in vitro development of SCNT embryos to the blastocyst stage, resulting in the production of viable cloned miniature pigs.

Recently, vascular endothelial growth factor (VEGF) has been regarded as an important factor associated with not only follicle development but also meiotic competence of oocytes. However, the mechanism of how VEGF works is poorly understood. In this study, we investigated in vitro maturation (IVM) of oocytes from different sizes in the absence or presence of a VEGF receptor inhibitor, Axitinib. Cumulus-oocyte complexes (COC) were obtained from small follicles (SF; l