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Spermatogonial stem cells (SSCs) are at the foundation of the highly productive spermatogenic process that continuously produces male gametes throughout postnatal life. However, experimental evaluation of SSCs in postnatal testes is complicated because these cells are extremely rare and few defining morphology or biochemical characteristics are known. In this study, we used the spermatogonial transplantation functional assay, combined with fluorescence-activated cell sorting (FACS) analysis to identify cellular, biochemical and surface antigenic characteristics of SSCs in rat testes during development. Our results demonstrated that forward scatter [(FSc).sup.hi], side scatter [(SSc).sup.hi], mitochondria membrane potential [([DELTA][PSI]m).sup.1o], Ep-CAM+, Thy-1+, [beta]3-integrin+ stem cells in neonate rat testes become [SSc.sup.1o], [DELTA][PSI][h.sup.hi], Ep-CAM+, Thy-[1.sup.1o], [beta]3-integrin- stem cells in pup rat testes. Furthermore, prospective identification of rat testis cell populations (Ep-CAM+), highly enriched for SSCs (1 in 13 for neonate; 1 in 8.5 for pup) enabled us to predict the Thy-1 and [beta]3-integrin status of stem cells in neonate and pup testes, which was subsequently confirmed by transplantation analyses. Systematic characterization of SSCs enabled the production of testis cell populations highly enriched (up to 120-fold) for SSCs and will facilitate future investigations of functional and genomic characteristics. Keywords: Stem cell; Spermatogonial stem cell; Spermatogenesis; Germline; Development; Rat; Transplantation; Testis; Enrichment

Adult tissue stem cells self-renew and differentiate in a way that exactly meets the biological demand of the dependent tissue. We evaluated spermatogonial stem cell (SSC) activity in the developing rat testis and the quality and accessibility of the stem cell niche in wild type, and two busulfan-treated models of rat pup recipient testes using an SSC transplantation technique as a functional assay. While our results revealed a 69-fold increase in stem cell activity during rat testis development from neonate to adult, only moderate changes in SSC concentration were observed, and stem cells from neonate, pup, and adult donor testes produce spermatogenic colonies of similar size. Analysis of the stem cell niche in recipient rat testes demonstrated that pup testes support high levels of donor stem cell engraftment when endogenous germ cells are removed or compromised by busulfan treatment. Fertility was established when rat pup donor testis cells were transplanted into fetal- or pup-busulfan-treated recipient rat pup testes, and the donor genotype was transmitted to subsequent generations. These results provide insight into stem cell/niche interactions in the rat testis and demonstrate that techniques originally developed in mice can be extended to other species for regenerative medicine and germline modification. Keywords: Stem cell; Spermatogonial stem cell; Niche; Spermatogenesis; Development; Rat; Fertility; Transplantation; Testis

Since the birth of the first child conceived via in vitro fertilization 40 years ago, fertility treatments and assisted reproductive technology have allowed many couples to reach their reproductive goals. As of yet, no fertility options are available for men who cannot produce functional sperm, but many experimental therapies have demonstrated promising results in animal models. Both autologous (stem cell transplantation, de novo morphogenesis, and testicular tissue grafting) and outside-the-body (xenografting and in vitro spermatogenesis) approaches exist for restoring sperm production in infertile animals with varying degrees of success. Once safety profiles are established and an ideal patient population is chosen, some of these techniques may be ready for human experimentation in the near future, with likely clinical implementation within the next decade. [ABSTRACT FROM AUTHOR]

Testicular tissue cryopreservation (TTC) provides an experimental option for fertility preservation for male children at significant risk for azoospermia owing to high-risk gonadotoxic treatments. A single institution, retrospective review of TTC cases from 2015 to 2017. Children at significant risk for azoospermia were eligible for study inclusion. A unilateral wedge biopsy of the testis was performed for TTC. TTC was performed in 23 patients. Average age was 10 years old (5 months to 18 years). Diagnoses included solid tumor (74%, n = 17), hematologic malignancy (17%, n = 4), and benign hematologic disease (13%, n = 3). Six patients had TTC at the time of disease relapse. Nine patients were referred for TTC prior to stem cell transplantation. The majority (70%, n = 16) of patients had an additional procedure at the time of TTC. One patient developed postoperative scrotal cellulitis that was treated with antibiotics. The majority of patients (96%, n = 22) had normal testicular tissue with the presence of germ cells on histopathological analysis. Median time to start of medical therapy was seven days with no unanticipated treatment delays. Testicular wedge biopsy for TTC can be performed safely, coordinated with other necessary procedures, and does not delay the start of treatment. TTC remains an experimental option for fertility preservation for children, as no spermatogenic recovery or pregnancies from cryopreserved testicular tissues have been reported to date. IV. [ABSTRACT FROM AUTHOR]

Abstract Many benign and malignant conditions require gonadotoxic treatment regimens that may threaten a child or adolescent's future fertility. Both males and females who have undergone gonadotoxic regimens are more likely to be infertile or have difficulty getting pregnant when compared to their siblings, however the desire to parent in the future is a priority. All children who are at risk of infertility should receive a fertility preservation (FP) consultation before treatment begins. We present a case report of a prepubertal boy who was diagnosed with osteosarcoma. His initial chemotherapeutic regimen did not qualify him for a FP procedure, but when he relapsed, his subsequent therapy did. Due to his peripubertal status he attempted sperm banking, a non-experimental FP method, but was azoospermic. He ultimately achieved success with a combination of testicular tissue cryopreservation and testicular sperm extraction, experimental FP procedures. What follows is a discussion of available FP options for peripubertal males and the current state of research for male fertility restoration. [ABSTRACT FROM AUTHOR]

Nutrient starvation drives yeast meiosis, whereas retinoic acid (RA) is required for mammalian meiosis through its germline target Stra8. Here, by using single-cell transcriptomic analysis of wild-type and Stra8 -deficient juvenile mouse germ cells, our data show that the expression of nutrient transporter genes, including Slc7a5 , Slc38a2 , and Slc2a1 , is downregulated in germ cells during meiotic initiation, and this process requires Stra8, which binds to these genes and induces their H3K27 deacetylation. Consequently, Stra8 -deficient germ cells sustain glutamine and glucose uptake in response to RA and exhibit hyperactive mTORC1/protein kinase A (PKA) activities. Importantly, expression of Slc38a2, a glutamine importer, is negatively correlated with meiotic genes in the GTEx dataset, and Slc38a2 knockdown downregulates mTORC1/PKA activities and induces meiotic gene expression. Thus, our study indicates that RA via Stra8, a chordate morphogen pathway, induces meiosis partially by generating a conserved nutrient restriction signal in mammalian germ cells by downregulating their nutrient transporter expression. [Display omitted] • Mouse germ cells withdraw nutrient transporter expression during meiotic initiation • This process is mediated by retinoic acid via its germline target Stra8 • Knockdown of Slc38a2, a glutamine importer, inhibits mTORC1/PKA activities • Slc38a2 knockdown or mTORC1/PKA inhibition activates meiotic gene expression Nutrient restriction induces meiosis in yeast. Here, Zhang et al. show that chordate morphogen retinoic acid via its germline target Stra8 induces downregulation of nutrient transporter expression during meiotic initiation in male mouse germ cells, thereby eliciting a conserved nutrient restriction signal including mTORC1/PKA inactivation to activate meiotic gene expression. [ABSTRACT FROM AUTHOR]

Spermatogonial stem cells (SSCs) in the testis support the lifelong production of sperm. SSCs reside within specialized microenvironments called "niches," which are essential for SSC self-renewal and differentiation. However, our understanding of the molecular and cellular interactions between SSCs and niches remains incomplete. Here, we combine spatial transcriptomics, computational analyses, and functional assays to systematically dissect the molecular, cellular, and spatial composition of SSC niches. This allows us to spatially map the ligand-receptor (LR) interaction landscape in both mouse and human testes. Our data demonstrate that pleiotrophin regulates mouse SSC functions through syndecan receptors. We also identify ephrin-A1 as a potential niche factor that influences human SSC functions. Furthermore, we show that the spatial re-distribution of inflammation-related LR interactions underlies diabetes-induced testicular injury. Together, our study demonstrates a systems approach to dissect the complex organization of the stem cell microenvironment in health and disease. [Display omitted] • Inference of ligand-receptor (LR) pairs at the spermatogonial stem cell niche • PTN and EPHA1 are potential niche factors • Spatial alteration of LR pair expression underlies diabetes-induced infertility Rajachandran et al. demonstrate how spatial transcriptomics can be leveraged to identify niche factors that regulate spermatogonial stem cell functions by mapping the ligand-receptor interaction landscape in mouse and human testes. [ABSTRACT FROM AUTHOR]

Summary The developmental origins of most adult stem cells are poorly understood. Here, we report the identification of a transcription factor—RHOX10—critical for the initial establishment of spermatogonial stem cells (SSCs). Conditional loss of the entire 33-gene X-linked homeobox gene cluster that includes Rhox10 causes progressive spermatogenic decline, a phenotype indistinguishable from that caused by loss of only Rhox10 . We demonstrate that this phenotype results from dramatically reduced SSC generation. By using a battery of approaches, including single-cell-RNA sequencing (scRNA-seq) analysis, we show that Rhox10 drives SSC generation by promoting pro-spermatogonia differentiation. Rhox10 also regulates batteries of migration genes and promotes the migration of pro-spermatogonia into the SSC niche. The identification of an X-linked homeobox gene that drives the initial generation of SSCs has implications for the evolution of X-linked gene clusters and sheds light on regulatory mechanisms influencing adult stem cell generation in general. [ABSTRACT FROM AUTHOR]

Infertility is a prevalent condition that has insidious impacts on the infertile individuals, their families, and society, which extend far beyond the inability to have a biological child. Lifestyle changes, fertility treatments, and assisted reproductive technology (ART) are available to help many infertile couples achieve their reproductive goals. All of these technologies require that the infertile individual is able to produce at least a small number of functional gametes (eggs or sperm). It is not possible for a person who does not produce gametes to have a biological child. This review focuses on the infertile man and describes several stem cell-based methods and gene therapy approaches that are in the research pipeline and may lead to new fertility treatment options for men with azoospermia. [ABSTRACT FROM AUTHOR]

Summary: Historically, spontaneous deletions and insertions have provided means to probe germline developmental genetics in Drosophila, mouse and other species. Here, induced pluripotent stem cell (iPSC) lines were derived from infertile men with deletions that encompass three Y chromosome azoospermia factor (AZF) regions and are associated with production of few or no sperm but normal somatic development. AZF-deleted iPSC lines were compromised in germ cell development in vitro. Undifferentiated iPSCs transplanted directly into murine seminiferous tubules differentiated extensively to germ-cell-like cells (GCLCs) that localized near the basement membrane, demonstrated morphology indistinguishable from fetal germ cells, and expressed germ-cell-specific proteins diagnostic of primordial germ cells. Alternatively, all iPSCs that exited tubules formed primitive tumors. iPSCs with AZF deletions produced significantly fewer GCLCs in vivo with distinct defects in gene expression. Findings indicate that xenotransplantation of human iPSCs directs germ cell differentiation in a manner dependent on donor genetic status. [Copyright &y& Elsevier]

Summary: Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have been shown to differentiate into primordial germ cells (PGCs) but not into spermatogonia, haploid spermatocytes, or spermatids. Here, we show that hESCs and hiPSCs differentiate directly into advanced male germ cell lineages, including postmeiotic, spermatid-like cells, in vitro without genetic manipulation. Furthermore, our procedure mirrors spermatogenesis in vivo by differentiating PSCs into UTF1-, PLZF-, and CDH1-positive spermatogonia-like cells; HIWI- and HILI-positive spermatocyte-like cells; and haploid cells expressing acrosin, transition protein 1, and protamine 1 (proteins that are uniquely found in spermatids and/or sperm). These spermatids show uniparental genomic imprints similar to those of human sperm on two loci: H19 and IGF2. These results demonstrate that male PSCs have the ability to differentiate directly into advanced germ cell lineages and may represent a novel strategy for studying spermatogenesis in vitro. [ABSTRACT FROM AUTHOR]

Think about 6 loved ones of reproductive age in your life. Now imagine that 1 of these 6 individuals is suffering from infertility. Perhaps they feel alone and isolated, unable to discuss their heartbreak with their closest friends, family, and support network. Suffering in silence. In this editorial, we discuss the infertility journey through the lens of the patients, the providers, and the scientists who struggle with infertility each and every day. Our goal is to open a dialogue surrounding infertility, with an emphasis on dismantling the longstanding societal barriers to acknowledging male infertility as a disease. Through education, communication, compassion, and advocacy, together we can all begin to break the deafening silence of male infertility. [ABSTRACT FROM AUTHOR]

Objective To determine the molecular characteristics of human spermatogonia and optimize methods to enrich spermatogonial stem cells (SSCs). Design Laboratory study using human tissues. Setting Research institute. Patient(s) Healthy adult human testicular tissue. Intervention(s) Human testicular tissue was fixed or digested with enzymes to produce a cell suspension. Human testis cells were fractionated by fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS). Main Outcome Measure(s) Immunostaining for selected markers, human-to-nude mouse xenotransplantation assay. Result(s) Immunohistochemistry costaining revealed the relative expression patterns of SALL4, UTF1, ZBTB16, UCHL1, and ENO2 in human undifferentiated spermatogonia as well as the extent of overlap with the differentiation marker KIT. Whole mount analyses revealed that human undifferentiated spermatogonia (UCHL1+) were typically arranged in clones of one to four cells whereas differentiated spermatogonia (KIT+) were typically arranged in clones of eight or more cells. The ratio of undifferentiated-to-differentiated spermatogonia is greater in humans than in rodents. The SSC colonizing activity was enriched in the THY1dim and ITGA6+ fractions of human testes sorted by FACS. ITGA6 was effective for sorting human SSCs by MACS; THY1 and EPCAM were not. Conclusion(s) Human spermatogonial differentiation correlates with increased clone size and onset of KIT expression, similar to rodents. The undifferentiated-to-differentiated developmental dynamics in human spermatogonia is different than rodents. THY1, ITGA6, and EPCAM can be used to enrich human SSC colonizing activity by FACS, but only ITGA6 is amenable to high throughput sorting by MACS. [ABSTRACT FROM AUTHOR]

Improved therapies for cancer and other conditions have resulted in a growing population of long-term survivors. Infertility is an unfortunate side effect of some cancer therapies that impacts the quality of life of survivors who are in their reproductive or prereproductive years. Some of these patients have the opportunity to preserve their fertility using standard technologies that include sperm, egg, or embryo banking, followed by IVF and/or ET. However, these options are not available to all patients, especially the prepubertal patients who are not yet producing mature gametes. For these patients, there are several stem cell technologies in the research pipeline that may give rise to new fertility options and allow infertile patients to have their own biological children. We will review the role of stem cells in normal spermatogenesis as well as experimental stem cell–based techniques that may have potential to generate or regenerate spermatogenesis and sperm. We will present these technologies in the context of the fertility preservation paradigm, but we anticipate that they will have broad implications for the assisted reproduction field. [ABSTRACT FROM AUTHOR]

Objective: To examine gonadal protective properties of granulocyte colony-stimulating factor (G-CSF) alone or in combination with stem cell factor (SCF) in female mice treated with high-dose alkylating chemotherapy. Design: Experimental laboratory animal study. Setting: Tertiary care academic hospital and research institute. Animal(s): Six- and 8-week-old C57B1/6 female mice. Intentention(s): Adult female mice were treated with [1] cyclophosphamide and busulfan (CTx), [2] CTx + G-CSF/SCF, [3] CTx + G-CSF, or [4] normal saline and dimethyl sulfoxide (DMSO; vehicle control). Main Outcome Measure(s): Follicle counts, microvessel density, cellular response to DNA damage, and litter production. Result(s): G-CSF ± SCF increased microvessel density and decreased follicle loss in CTx-treated female mice compared with CTx-only treated female mice. Mice administered CTx alone exhibited premature ovarian insufficiency, with only 28% of mice producing two litters. However, 100% of mice receiving CTx with G-CSF + SCF, and 80% of mice receiving CTx + G-CSF alone produced at least three litters and 20% of mice in each group produced five litters. Conclusion(s): Treatment of mice with G-CSF decreases chemotherapy-induced ovarian follicle loss and extends time to premature ovarian insufficiency in female mice. Further studies are needed to validate these preclinical results in humans and compare efficacy with the established GnRH analogue treatments. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate gonadal-protective properties of thalidomide in a mouse model of chemotherapy-induced ovarian failure. Administration of thalidomide before alkylating chemotherapy preserved ovarian follicles and lead to the resumption of normal estrous cyclicity. [ABSTRACT FROM AUTHOR]

Aging men display reduced reproductive health; however, testis aging is poorly understood at the molecular and genomic levels. Here, we utilized single-cell RNA-seq to profile over 44,000 cells from both young and older men and examined age-related changes in germline development and in the testicular somatic cells. Age-related changes in spermatogonial stem cells appeared modest, whereas age-related dysregulation of spermatogenesis and somatic cells ranged from moderate to severe. Altered pathways included signaling and inflammation in multiple cell types, metabolic signaling in Sertoli cells, hedgehog signaling and testosterone production in Leydig cells, cell death and growth in testicular peritubular cells, and possible developmental regression in both Leydig and peritubular cells. Remarkably, the extent of dysregulation correlated with body mass index in older but not in younger men. Collectively, we reveal candidate molecular mechanisms underlying the complex testicular changes conferred by aging and their possible exacerbation by concurrent chronic conditions such as obesity. [Display omitted] • A transcriptional single-cell atlas of testes from older men • Age-related changes in SSCs are modest • Age-related dysregulation of spermatogenesis and somatic cells are pronounced • Dysregulation correlated with BMI in older but not younger men Guo, Cairns, and colleagues revealed aging-related alternations of human germ cells and testicular somatic cells through single-cell transcriptomic profiling, providing candidate molecular mechanisms underlying the complex testicular changes conferred by aging and their possible exacerbation by concurrent chronic conditions such as obesity. [ABSTRACT FROM AUTHOR]

Spermatogenesis is a highly regulated process that produces sperm to transmit genetic information to the next generation. Although extensively studied in mice, our current understanding of primate spermatogenesis is limited to populations defined by state-specific markers from rodent data. As between-species differences have been reported in the duration and differentiation hierarchy of this process, it remains unclear how molecular markers and cell states are conserved or have diverged from mice to man. To address this challenge, we employ single-cell RNA sequencing to identify transcriptional signatures of major germ and somatic cell types of the testes in human, macaque, and mice. This approach reveals similarities and differences in expression throughout spermatogenesis, including the stem/progenitor pool of spermatogonia, markers of differentiation, potential regulators of meiosis, RNA turnover during spermatid differentiation, and germ cell-soma communication. These datasets provide a rich foundation for future targeted mechanistic studies of primate germ cell development and in vitro gametogenesis. • A multispecies scRNA analysis identifies conserved and divergent cell states • Functional characterization of a TSPAN33+ SPG population by xenotransplantation • Receptor-ligand pairs show divergent germline-soma communications Spermatogenesis has been studied extensively in rodents, but the conservation among species is not well understood. Shami et al. employ single-cell RNA sequencing to compare transcriptional signatures of thousands of testes cells from human, macaque, and mouse, creating a resource to advance understanding of mammalian reproduction and evolution. [ABSTRACT FROM AUTHOR]

Objective To illustrate the step-by-step protocol followed to assay germ cell transplantation into the seminiferous epithelium of mouse testes. Design Video presentation of an animal model for research in reproductive and regenerative medicine. Setting Research laboratory. Animal(s) Male nude mice (NU-Foxn1 nu ). Intervention(s) Mice were chemically sterilized with alkylant compounds (busulfan) followed by gonadal microsurgery to inject donor germ cells. Main Outcome Measure(s) Donor cells should be labeled with reporter genes, such as green fluorescent protein (GFP), lactose operon (LacZ), or alternatively design an effective strategy with specific antibodies to track them within the recipient testes. Sperm detection in the ejaculate can also be used as a read out. However, in this case detection of the donor genotype in the sperm is mandatory to elucidate their origin. Result(s) In the present study we describe the complete protocol for germ cell transplant by efferent duct injection, including the preparation of recipient mice, surgery for the germ cell transplant, and analysis of recipient testes. The main strength of this technique is that it constitutes the gold standard for a functional test of the germ cell potential as only spermatogonial stem cells are able to properly colonize the seminal lumen. Both fresh and frozen/thawed testicular cells are suitable for this technique as donor germ cells. Also, enrichment of living spermatogonial stem cells, previous to the transplant, seems to improve the efficiency of colonization. For proper colonization of germ cells, the niche should be available and thus mouse strains that lack endogenous spermatogenesis such as W/W v mutant mice are usually used. In the case of nonmatched donor cells, seminiferous epithelium of immune-suppressed recipient mice should be germ cell depleted before the transplant. One limitation of this technique is that the procedure can take up to 3 months. Also, in contrast to the full recovery of spermatogenesis in mouse-to-mouse transplants, xenotransplantation of germ cells from phylogenetically distant species, such as humans into mouse recipients, results in colonization of donor cells and spermatogonial expansion, but fail in their spermatogenic progression due to evolutive incompatibilities with the recipient niche. Xenografting of pieces of donor testis tissue under the skin of mouse hosts is an alternative approach that is currently being investigated to try to solve this limitation. Conclusion(s) Transplantation of spermatogonial stem cells into the seminal lumen of mouse testes is a functional assay that defines this cellular subpopulation by its ability to colonize it. This technique can be used as a model to elucidate the insights of spermatogonial stem cells, to produce transgenic animals by genetically manipulating donor cells before transplantation, but also it has potential applications in fertility preservation in cattle and humans as it is feasible in large animals, as recent reports have demonstrated with rhesus monkeys, that recovered spermatogenesis after allogenic transplantation, and even from human cadaver testes. Therefore spermatogonial stem cells isolated from prepuberal boys, who are treated with alkylant chemotherapy, could be returned to their testis to regenerate spermatogenesis in the future. [ABSTRACT FROM AUTHOR]