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COMMENTS ON PROFESSOR RAMSEYER'S ARTICLE, DO SCHOOL CLIQUES DOMINATE JAPANESE BUREAUCRACIES? EVIDENCE FROM SUPREME COURT APPOINTMENTS On September 11, 2010, I received an e-mail from a graduate of my seminar. [...]

During development, the retinal vasculature grows toward hypoxic areas in an organized fashion. By contrast, in ischemic retinopathies, new blood vessels grow out of the retinal surfaces without ameliorating retinal [...]

The neural fate is generally considered to be the intrinsic direction of embryonic stem (ES) cell differentiation. However, little is known about the intracellular mechanism that leads undifferentiated cells to adopt the neural fate in the absence of extrinsic inductive signals. Here we show that the zinc-finger nuclear protein Zfp521 is essential and sufficient for driving the intrinsic neural differentiation of mouse ES cells. In the absence of the neural differentiation inhibitor BMP4, strong Zfp521 expression is intrinsically induced in differentiating ES cells. Forced expression of Zfp521 enables the neural conversion of ES cells even in the presence of BMP4. Conversely, in differentiation culture, Zfp521-depleted ES cells do not undergo neural conversion but tend to halt at the epiblast state. Zfp521 directly activates early neural genes by working with the co-activator p300. Thus, the transition of ES cell differentiation from the epiblast state into neuroectodermal progenitors specifically depends on the cell-intrinsic expression and activator function of Zfp521., Previous studies, particularly in amphibians, have demonstrated that the initial step of vertebrate neural differentiation from uncommitted embryonic ectodermal cells occurs via a cell-intrinsic mechanism and requires only that inhibitory [...]

Emerging evidence indicates that the tight communication between vascular endothelial cells and mural cells using platelet-derived growth factor (PDGF)-BB is essential for capillary stabilization during the angiogenic process. However, little is known about the related regulator that determines PDGF-BB expression. Using murine models of therapeutic neovascularization, we here show that a typical lymphangiogenic factor, vascular endothelial growth factor (VEGF)-C, is an essential regulator determining PDGF-BB expression for vascular stabilization via a paracrine mode of action. The blockade of VEGF type 3 receptor (VEGFR3) using neutralizing antibody AFL-4 abrogated FGF-2-mediated limb salvage and blood flow recovery in severely ischemic hindlimb. Interestingly, inhibition of VEGFR3 activity not only diminished lymphangiogenesis, but induced marked dilatation of capillary vessels, showing mural cell dissociation. In these mice, VEGF-C and PDGF-B were upregulated in the later phase after induced ischemia, on day 7, when exogenous FGF-2 expression had already declined, and blockade of VEGFR3 or PDGF-BB activities diminished PDGF-B or VEGF-C expression, respectively. These results clearly indicate that VEGF-C is a critical mediator, not only for lymphangiogenesis, but also for capillary stabilization, the essential molecular mechanism of communication between endothelial cells and mural cells during neovascularization. vascular endothelial growth factor-C; platelet-derived growth factor-BB; lymphangiogenesis; capillary stabilization doi: 10.1152/ajpheart.00015.2009.

Blood lines How the blood system forms during embryonic development is a topic of intensive research, in part because of the potential importance of the process for regenerative medicine. Two main theories have emerged to explain the formation of the haematopoietic stem cells that eventually populate the adult born marrow. One idea is that the haematopoietic stem cell and the endothelial lineage arise independently from the mesoderm; the other is that some haematopoietic and endothelial lineages derive from a specialized progenitor called a haemangioblast. Three papers in this issue unify the two theories. Both are correct: the haemangioblast does generate haematopoietic cells, but via a haemogenic endothelium intermediate. Recent studies have indicated that embryonic blood is produced by endothelial cells, which also form blood vessels and arteries. This paper uses a direct imaging and cell tracking approach to directly show that embryonic endothelial cells do produce blood. By imaging cells over days, they were able to show that a subset of embryonic endothelial cells formed blood cells. Despite decades of research, the identity of the cells generating the first haematopoietic cells in mammalian embryos is unknown.sup.1. Indeed, whether blood cells arise from mesodermal cells, mesenchymal progenitors, bipotent endothelial-haematopoietic precursors or haemogenic endothelial cells remains controversial.sup.2,3,4,5,6,7,8,9. Proximity of endothelial and blood cells at sites of embryonic haematopoiesis, as well as their similar gene expression, led to the hypothesis of the endothelium generating blood. However, owing to lacking technology.sup.10 it has been impossible to observe blood cell emergence continuously at the single-cell level, and the postulated existence of haemogenic endothelial cells remains disputed.sup.1. Here, using new imaging and cell-tracking methods, we show that embryonic endothelial cells can be haemogenic. By continuous long-term single-cell observation of mouse mesodermal cells generating endothelial cell and blood colonies, it was possible to detect haemogenic endothelial cells giving rise to blood cells. Living endothelial and haematopoietic cells were identified by simultaneous detection of morphology and multiple molecular and functional markers. Detachment of nascent blood cells from endothelium is not directly linked to asymmetric cell division, and haemogenic endothelial cells are specified from cells already expressing endothelial markers. These results improve our understanding of the developmental origin of mammalian blood and the potential generation of haematopoietic stem cells from embryonic stem cells., Author(s): Hanna M. Eilken [sup.1] , Shin-Ichi Nishikawa [sup.2] , Timm Schroeder [sup.1] Author Affiliations: (1) Institute of Stem Cell Research, Helmholtz Center Munich--German Research Center for Environmental Health (GmbH), [...]

Despite decades of research, the identity of the cells generating the first haematopoietic cells in mammalian embryos is unknown (1). Indeed, whether blood cells arise from mesodermal cells, mesenchymal progenitors, bipotent endothelial-haematopoietic precursors or haemogenic endothelial cells remains controversial (2-9). Proximity of endothelial and blood cells at sites of embryonic haematopoiesis, as well as their similar gene expression, led to the hypothesis of the endothelium generating blood. However, owing to lacking technology (10) it has been impossible to observe blood cell emergence continuously at the single-cell level, and the postulated existence of haemogenic endothelial cells remains disputed (1). Here, using new imaging and cell-tracking methods, we show that embryonic endothelial cells can be haemogenic. By continuous long-term single-cell observation of mouse mesodermal cells generating endothelial cell and blood colonies, it was possible to detect haemogenic endothelial cells giving rise to blood cells. Living endothelial and haematopoietic cells were identified by simultaneous detection of morphology and multiple molecular and functional markers. Detachment of nascent blood cells from endothelium is not directly linked to asymmetric cell division, and haemogenic endothelial cells are specified from cells already expressing endothelial markers. These results improve our understanding of the developmental origin of mammalian blood and the potential generation of haematopoietic stem cells from embryonic stem cells., It has previously been shown that embryonic cells expressing endothelial molecules can generate blood (3,8,11,12). However, only single markers were used at single time points, and transition of single endothelial [...]

BAFF-R-dependent activation of the alternative NF-KB pathway plays an essential role in mature B cell survival. Mutations leading to overexpression of NIK and deletion of the TRAF3 gene are implicated in human multiple myeloma. We show that overexpression of NIK in mouse B lymphocytes amplifies alternative NF-KB activation and peripheral B cell numbers in a BAFF-R-dependent manner, whereas uncoupling NIK from TRAF3-mediated control causes maximal plO0 processing and dramatic hyperplasia of BAFF-R-independent B cells. NIK controls alternative NF-KB signaling by increasing the protein levels of its negative regulator TRAF3 in a dose-dependent fashion. This mechanism keeps NIK protein levels below detection even when they cause B cell hyperplasia, so that contributions of NIK to B cell pathologies can easily be overlooked. IKB kinase | NF-KB | Hyperplasia | p100 processing | knockin

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2007.04.028 Byline: Yasuhiro Takashima (1)(3), Takumi Era (1), Kazuki Nakao (2), Saki Kondo (4), Masato Kasuga (3), Austin G. Smith (5), Shin-Ichi Nishikawa (1) Keywords: STEMCELL Abstract: Mesenchymal stem cells (MSCs) are defined as cells that undergo sustained in vitro growth and are able to give rise to multiple mesenchymal lineages. Although MSCs are already used in regenerative medicine little is known about their in vivo behavior and developmental derivation. Here, we show that the earliest wave of MSC in the embryonic trunk is generated from Sox1.sup.+ neuroepithelium but not from mesoderm. Using lineage marking by direct gfp knock-in and Cre-recombinase mediated lineage tracing, we provide evidence that Sox1.sup.+ neuroepithelium gives rise to MSCs in part through a neural crest intermediate stage. This pathway can be distinguished from the pathway through which Sox1.sup.+ cells give rise to oligodendrocytes by expression of PDGFR[beta] and A2B5. MSC recruitment from this pathway, however, is transient and is replaced by MSCs from unknown sources. We conclude that MSC can be defined as a definite in vivo entity recruited from multiple developmental origins. Author Affiliation: (1) Laboratory for Stem Cell Biology, Riken Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, 650-0047, Japan (2) Laboratory for Animal Resources and Genetic Engineering, Riken Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, 650-0047, Japan (3) Department of Clinical Molecular Medicine, Division of Diabetes and Digestive and Kidney Diseases, Kobe University Graduate School of Medicine, 7-5-1 Kusunokimachi, Chuo-ku, Kobe, 650-0017, Japan (4) Laboratory of Molecular Genetics, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan (5) Institute for Stem Cell Biology, University of Cambridge, Cambridge, CB2, 1QT, UK Article History: Received 14 September 2006; Revised 16 February 2007; Accepted 9 April 2007 Article Note: (miscellaneous) Published: June 28, 2007

Melanoblasts (Mbs) are thought to be strictly regulated by cell-cell interactions with epidermal keratinocytes, although the precise molecular mechanism of the regulation has been elusive. Notch signaling, whose activation is mediated by cell-cell interactions, is implicated in a broad range of developmental processes. We demonstrate the vital role of Notch signaling in the maintenance of Mbs, as well as melanocyte stem cells (MSCs). Conditional ablation of Notch signaling in the melanocyte lineage leads to a severe defect in hair pigmentation, followed by intensive hair graying. The defect is caused by a dramatic elimination of Mbs and MSCs. Furthermore, targeted overexpression of Hes1 is sufficient to protect Mbs from the elimination by apoptosis. Thus, these data provide evidence that Notch signaling, acting through Hes1, plays a crucial role in the survival of immature Mbs by preventing initiation of apoptosis.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.12.016 Byline: Atsushi Takebe (a)(c), Takumi Era (a), Mitsuhiro Okada (a)(b), Lars Martin Jakt (a)(b), Yoshikazu Kuroda (c), Shin-Ichi Nishikawa (a) Keywords: ES cell; In vitro differentiation; DNA microarray; PDGFR[alpha]; ARID3b Abstract: An inherent difficulty in using DNA microarray technology on the early mouse embryo is its relatively small size. In this study, we investigated whether use of ES cell differentiation culture, which has no theoretical limit in the number of cells that can be generated, can improve this situation. Seven distinct ES-cell-derived populations were analyzed by DNA microarray and examined for genes whose distribution patterns are similar to those of PDGFR[alpha], a gene implicated in differentiation of mesoderm/mesenchymal lineages. Using software developed in our laboratory, we formed a group of 30 genes which showed the highest similarity to PDGFR[alpha], 18 of these genes were shown to be involved in development of either mesodermal, mesenchymal or neural crest cells. This list also contains several genes whose role in embryogenesis has not yet been fully identified. One such molecule is mARID3b. The mARID3b expression is found in the paraxial mesoderm and cranial mesenchyme. mARID3b-null mouse showed early embryonic lethality, and most phenotypes of this mutant appear to develop from a failure to generate a sufficient number of cranial mesenchymal cells. These results demonstrate the potential use of ES cell differentiation culture in identifying novel genes playing an indispensable role in embryogenesis. Author Affiliation: (a) Laboratory for Stem Cell Biology, RIKEN Center for Development Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan (b) The Foundation for Biomedical Research and Innovation, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan (c) Division of Gastroenterological Surgery, Graduate School of Medicine, Kobe University, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, Hyogo 650-0017, Japan Article History: Received 27 June 2005; Revised 18 November 2005; Accepted 6 December 2005

Identification of novel genes that are similar to platelet-derived growth factor receptor, using DNA microarray studies on mouse embryonic cells, to find their role in embryogenesis is presented.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.12.025 Byline: Siu-Shan Mak (a), Mariko Moriyama (a), Eri Nishioka (b), Masatake Osawa (a), Shin-Ichi Nishikawa (a) Keywords: bcl2; bcl2 null; Melanoblast; c-Kit; Hair follicle development; Melanocyte stem cell; Melanocyte survival; Stem cell development; Stem cell factor Abstract: Bcl2 null mice display a characteristic loss of pigmentation demonstrating the importance of Bcl2 in the melanocyte (Mc) lineage. It was recently reported that this abnormal phenotype is due to the failure of melanocyte stem cell (MSC) maintenance and that Bcl2 is selectively important for the survival of MSCs. However, in our analysis of the same mouse, we observe a reduction in melanoblast (Mb) number in both epidermal and follicular populations. More importantly, there is a complete absence of MSCs. SCF downregulation in the epidermis is concomitant with the dramatic reduction in Mb numbers observed in the Bcl2 null, suggesting that Bcl2 is indispensable for the survival of Mbs in the absence of c-Kit signaling. Consistently, abrogation of c-Kit signaling in Bcl2 null mice depletes all Mbs and Mcs, whereas continuous expression of SCF in epidermal keratinocytes rescues the MSCs. Our results demonstrate that Bcl2 has a general role in Mb and Mc survival and is essential for the emergence of MSCs. Moreover, the results indicate that the first wave of Mcs that provide hair pigmentation is derived directly from epidermal Mbs bypassing MSCs. Furthermore, a Bcl2-independent mechanism of action of SCF in the Mc lineage is revealed as SCF c-Kit signaling is functional in the absence of Bcl2. Author Affiliation: (a) RIKEN, Center for Developmental Biology (CDB), Laboratory for Stem Cell Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan (b) Division of Dermatology, Department of Clinical Molecular Medicine, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan Article History: Received 29 July 2005; Revised 6 December 2005; Accepted 9 December 2005

Using a study on mice, the importance of Bcl2 in the survival of melanoblasts and melanocytes and in formation of melanocyte stem cells, all of which are required for hair follicle development and hair pigmentation, is examined.

Recent findings have shown that embryonic vascular progenitor cells are capable of differentiating into mural and endothelial cells. However, the molecular mechanisms that regulate their differentiation, proliferation, and endothelial sheet formation remain to be elucidated. Here, we show that members of the transforming growth factor (TGF)-[beta] superfamily play important roles during differentiation of vascular progenitor cells derived from mouse embryonic stem cells (ESCs) and from 8.5-days postcoitum embryos. TGF-[beta] and activin inhibited proliferation and sheet formation of endothelial cells. Interestingly, SB-431542, a synthetic molecule that inhibits the kinases of receptors for TGF-[beta] and activin, facilitated proliferation and sheet formation of ESC-derived endothelial cells. Moreover, SB-431542 up-regulated the expression of claudin-5, an endothelial specific component of tight junctions. These results suggest that endogenous TGF-[beta] activin signals play important roles in regulating vascular growth and permeability.

Author(s): Daisuke Yamazaki [1, 2]; Shiro Suetsugu [1, 2]; Hiroaki Miki [3, 4]; Yuki Kataoka [5]; Shin-Ichi Nishikawa [6]; Takashi Fujiwara [7]; Nobuaki Yoshida [5]; Tadaomi Takenawa (corresponding author) [1, [...]

The transcription factor recombination signal sequence-binding protein J[kappa] (RBP-J) is a key downstream element in the signaling pathway of all four mammalian Notch receptors that are critically involved in the control of embryonic and adult development. RBP-J-deficient mice display complex defects and die around day 9.5 postcoitum. Here, we investigate the function of RBP-J in the development of mesodermal cell lineages by using the OP9 stroma coculture system. RBP-J-deficient embryonic stem (ES) cells gave rise to cardiomyocytes, endothelial cells, and primitive and definitive hematopoietic cells. Thus, RBP-J-mediated signals are not required for generation of these cell types. However, when compared with parental RBP-J-expressing ES cells, cardiomyogenesis derived from RBP-J-deficient ES cells was increased. Repression over the cardiogenic pathway was restored by expressing RBP-J in RBP-J-deficient ES cells. Our data indicate that Notch signaling via RBP-J plays an important role for the correct specification of myocardial cell fates.

The Foxl1 gene, which encodes a winged helix transcriptional regulator, is expressed in the mesenchymal layer of developing and mature gastrointestinal tract. Foxl1-deficient mice exhibit various defects not only in the epithelial layer of the gastrointestinal tract but also in gut-associated lymphoid tissues. In the small intestine of Foxl1-deficient mice, the formation of Peyer's patches is affected, particularly in the caudal region. This alteration is shown to be due to the delayed formation of Peyer's patches organizing centers as revealed by the expressions of VCAM1 and IL-7 receptor [alpha]-chain at 17.5 days postcoitus. Peyer's patch defects are concordant with the significantly decreased expression of Lymphotoxin [beta]-receptor in the caudal region of fetal intestine. Foxl1 is suggested to regulate the responsiveness of fetal intestinal mesenchymal cells to inductive signals mediated by Lymphotoxins during Peyer's patch organogenesis. In addition, constitutive outgrowth of colonic patches due to defects in radioresistant stromal components of colonic patches are seen in Foxl1-deficient mice. Because of the functional similarities of hypertrophic colonic patches to those seen in hapten-induced experimental colitis, this hypertrophy is suggested to involve Lymphotoxin [beta]-receptor signaling. Together, the data suggest that Foxl1 might be involved in cellular responses of gut-associated lymphoid tissues dependent upon the Lymphotoxins/Lymphotoxin [beta]-receptor axis. Keywords: Foxl1; Peyer's patch; Colonic patch; Gut mesenchyme; Lymphotoxins; Mouse

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is an adapter protein that links signals from members of the TNFR superfamily and Toll/IL-1 receptor family to activation of transcription factors NF[kappa]B and AP-1. Analysis of TRAF6-deficient mice revealed that TRAF6 is essential for normal bone formation and establishment of immune and inflammatory systems. Here we report that TRAF6 deficiency results in defective development of epidermal appendixes, including guard hair follicles, sweat glands, sebaceous glands of back skin, and modified sebaceous glands such as meibomian glands, anal glands, and preputial glands. Except the sebaceous gland impairment, these abnormal phenotypes are identical to those observed in Tabby (Ta), downless (dl), and crinkled (cr) mice, which are models of hypohidrotic (anhidrotic) ectodermal dysplasia in human. [beta]-catenin and mucosal addressin cell adhesion molecule-1, an early marker of developing guard-hair follicles is absent in the skin of TRAF6-deficient embryos. Thus, TRAF6 is essential for development of epidermal appendixes. TRAF6 does not associate with the cytoplasmic tail of the dl protein (DL)/ectodysplasin receptor (EDAR) receptor, which, when mutated, results in hypohidrotic (anhidrotic) ectodermal dysplasia. However, TRAF6 associates with X-linked ectodysplasin-A2 receptor (XEDAR) and TNFR super family expressed on the mouse embryo (TROY/toxicity and JNK inducer (TAJ), which are EDAR-related members of the TNFR superfamily that are expressed at high level in epidermal appendixes. Furthermore, TRAF6 is essential for the XEDAR-mediated NF[kappa]B activation. Our results suggest that TRAF6 may transduce signals emanating from XEDAR or TROY/TAJ that are associated with development of epidermal appendixes.

Author(s): Emi K. Nishimura [1, 2, 3]; Siobhán A. Jordan [4]; Hideo Oshima [3, 5]; Hisahiro Yoshida [1]; Masatake Osawa [6]; Mariko Moriyama [6]; Ian J. Jackson [4]; Yann Barrandon [...]

We previously identified a stromal cell-derived inducing activity (SDIA), which induces differentiation of neural cells, including midbrain tyrosine hydroxylase-positive T[H.sup.+] dopaminergic neurons, from mouse embryonic stem cells. We report here that SDIA induces efficient neural differentiation also in primate embryonic stem cells. Induced neurons contain T[H.sup.+] neurons at a frequency of 35% and produce a significant amount of dopamine. Interestingly, differentiation of T[H.sup.+] neurons from undifferentiated embryonic cells occurs much faster in vitro (10 days) than it does in the embryo ([approximately equal to]5 weeks). In addition, 8% of the colonies contain large patches of Pax[6.sup.+] - pigmented epithelium of the retina. The SDIA method provides an unlimited source of primate cells for the study of pathogenesis, drug development, and transplantation in degenerative diseases such as Parkinson's disease and retinitis pigmentosa.

Research has been conducted on the matrix metalloproteinase important for the extracellular matrix remodeling. Results indicate that membrane-anchored glycoprotein RECK regulates metalloproteinases involved in cancer progression and the results are reported.

The lymphatic vasculature transports extravasated tissue fluid, macromolecules and cells back into the blood circulation. Recent reports have focused on the molecular mechanisms regulating the lymphatic vessels. Vascular endothelial growth factor (VEGF)-C and VEGF-D have been shown to stimulate lymphangiogenesis and their receptor, VEGFR-3, has been linked to human hereditary lymphedema. Here we show that a soluble form of VEGFR-3 is a potent inhibitor of VEGF-C/VEGF-D signaling, and when expressed in the skin of transgenic mice, it inhibits fetal lymphangiogenesis and induces a regression of already formed lymphatic vessels, though the blood vasculature remains normal. Transgenic mice develop a lymphedema-like phenotype characterized by swelling of feet, edema and dermal fibrosis. They survive the neonatal period in spite of a virtually complete lack of lymphatic vessels in several tissues, and later show regeneration of the lymphatic vasculature, indicating that induction of lymphatic regeneration may also be possible in humans., Author(s): Taija Makinen [1]; Lotta Jussila [1]; Tanja Veikkola [1]; Terhi Karpanen [1]; Mikko I. Kettunen [2]; Kalevi J. Pulkkanen [3, 4]; Risto Kauppinen [2]; David G. Jackson [5]; Hajime [...]

Metastasis to local lymph nodes via the lymphatic vessels is a common step in the spread of solid tumors. To investigate the molecular mechanisms underlying the spread of cancer by the lymphatics, we examined the ability of vascular endothelial growth factor (VEGF)-D, a ligand for the lymphatic growth factor receptor VEGFR-3/Flt-4, to induce formation of lymphatics in a mouse tumor model. Staining with markers specific for lymphatic endothelium demonstrated that VEGF-D induced the formation of lymphatics within tumors. Moreover, expression of VEGF-D in tumor cells led to spread of the tumor to lymph nodes, whereas expression of VEGF, an angiogenic growth factor which activates VEGFR-2 but not VEGFR-3, did not. VEGF-D also promoted tumor angiogenesis and growth. Lymphatic spread induced by VEGF-D could be blocked with an antibody specific for VEGF-D. This study demonstrates that lymphatics can be established in solid tumors and implicates VEGF family members in determining the route of metastatic spread., Author(s): Steven A. Stacker (corresponding author) [1]; Carol Caesar [1]; Megan E. Baldwin [1]; Gillian E. Thornton [1]; Richard A. Williams [2]; Remko Prevo [3]; David G. Jackson [3]; Shin-ichi [...]

Author(s): Jun Yamashita (corresponding author) [1]; Hiroshi Itoh [1]; Masanori Hirashima [2]; Minetaro Ogawa [2]; Satomi Nishikawa [2]; Takami Yurugi [1]; Makoto Naito [3]; Kazuwa Nakao [1]; Shin-Ichi Nishikawa [2] [...]

Melanocytes (Mc) and their progenitors melanoblasts (Mb) are derived from the neural crest and migrate along the dorsolateral pathway to colonize the dermis, the epidermis, and finally the hair matrix. To examine the involvement of cadherins in the migration of Mc lineage cells, we combined flow cytometric analysis of dissociated live cells with immunohistochemical staining of tissue sections to quantify the level of cadherin expression on the surface of Mb/Mc. At 11.5 days postcoitum, Mb are in the dermis and are E-cadherin(super -)P-cadherin(super -) (E-cad(super -)P-cad(super -)). During the next 48 h, a 200-fold increase of E-cadherin expression is induced on the surface of Mb prior to their entry into the epidermis, thereby forming a homogeneous E-cad(super high)p-cad(super -/low) population. The cadherin expression pattern then diversifies, giving rise to three populations, an E-cad(super -)P-cad(super -) dermal population, E-cad(super high)P-cad(super low) epidermal population, and E-cad(super -)P-cad(super med.high) follicular population. In all three populations, the patterns of expression are region-specific, being identical with those of surrounding cells such as keratinocytes and fibroblasts, and are preserved before and after pigmentation. While most of the epidermal Mb/Mc disappear after the neonatal stage in normal mice, forced expression of steel factor in the epidermis of transgenic mice promotes survival of epidermal Mb/Mc, maintaining epidermal-type cadherin expression pattern (E-cad(super high)P-cad(super low)) throughout the postnatal life. These findings indicate the involvement of extrinsic cues in coordinating the cadherin expression pattern of Mb/Mc and suggest a role for E- and P-cadherins in guiding Mc progenitors to their final destinations. Key Words: melanocyte; melanoblast; cadherins; E-cadherin; P-cadherin; expression; migration; diversification; colonization; quantitative; qualitative; microenvironment; steel factor (SLF); flow cytometry; epidermis; dermis; hair follicles; hair matrix.

Afadin, a key molecule in structural organization of polarized epithelia cell-cell junctions in embryogenesis, is discussed. Afadin is essential for this organization. It is an actin filament-binding protein and binds to nectin, a cell adhesion molecule. Afadin is with nectin at cadherin-based cell-cell adherens junctions. Mice in which the afadin gene was disrupted by homologous recombination and embryonic stem cells were generated for the research.

Transcription factors with basic helix-loop-helix (HLF) motifs are essential for certain cell differentiation processes during multicellular organism development. The functions of the transcription factors are inhibited by Id proteins, by suppression of their heterodimerization partners vial the HLH domains. Id2 is found to be essential for normal development of mice, and is require for the generation of peripheral lymphoid organs and NK cells.

Mice lacking CXCR4, the cell surface receptor, were generated to elucidate the physiological functions of CXCR4. The functions of CXCR4 during embryogenesis were studied by developing embryos by in situ hybridization. CXCR4 and PBSF/SDF-1 were found to be responsible for the formation of a mature vascular system, supplying the gastrointestinal tract. The results suggested that CXCR4 is a main physiological receptor for PBSF/SDF-1.

Ovarian follicle development is controlled by the cycling variation of gonadotrophins derived from the central nervous system. Intragonadal signals are also required, especially in the autonomous development of small follicles. Receptor tyrosine kinase c-kit and its ligand SLF (Steel factor) are expressed on the surface of specific populations of follicle-forming cells in a contiguous manner and are thought to have important roles in follicular development. We blocked the interaction of c-kit and its ligand by administering the function-blocking antibody ACK2 to developing mice at various times after birth and monitored ovarian follicle development. A blockade of c-kit function disturbed the onset of primordial follicle development, primary follicle growth, follicular fluid formation of preantral follicles, and Penultimate-stage ovarian follicle maturation before ovulation. Ovarian follicle growth was dependent on c-kit during the first 5 days after birth when the functional FSH receptor is not yet expressed in mouse ovary. In contrast, primordial follicle formation and survival, small preantral or antral follicle development, ovulation, and luteinization of the ovulated follicle were not affected by this antibody. These findings indicate the stepwise requirement of c-kit and its ligand interaction system in the developing ovarian follicle and that c-kit with its ligand supports the autonomous development of ovarian follicle independent of gonadotrophins.

The effect of a rat anti-murine-Kit monoclonal body (ACK2)-induced impairment of the interstitial cell (IC) network on the contractile responses of the ileum was investigated. Electrophysiological experiments revealed that an impaired Kit-dependent IC network alters the contractile responses of the intestinal tract to pharmacological agents. It was suggested that the monoclonal antibodies impaired the Kit signaling pathway that is essential to the development of IC as pacemaker cells.

Pre-B-cell-growth-stimulating factor/stromal cell-derived factor-1 (PBSF/SDF-1), a member of the CXC group of chemokines, has an important physiological role in development. Mutant mice with disrupted gene encoding PBSF/SDF-1 die perinatally. The mutant embryos have reduced B-cell progenitors in both fetal liver and bone marrow, while they have reduced myeloid progenitors only in the bone marrow. This indicates that PBSF/SDF-1 regulates B-cell lymphopoiesis and bone-marrow myelopoiesis. The mutants also have a cardiac ventricular septal defect.

In this study, we describe the interaction between cytokine and cytokine receptor (R) for the activation and proliferation of [Gamma][Delta] T-cell receptor-positive T cells ([Gamma][Delta] T cells). [Gamma][Delta] T cells isolated from murine intestinal intraepithelial lymphocytes (IELs) were separated into [Gamma][[Delta].sup.Dim] and [Gamma][[Delta].sup.Bright] fractions according to the intensity of [Gamma][Delta] T-cell receptor expression. The [Gamma][[Delta].sup.Dim] T cells express low levels of IL-2R and IL-7R as shown by flow cytometry and reverse transcriptase-PCR analysis, whereas [Gamma][[Delta].sup.Bright] T cells did not express either receptor. Our study also revealed that recombinant murine (rm)IL-2 and rmIL-7 reciprocally induced high expressions of IL-7R and IL-2R, respectively, on [Gamma][[Delta].sup.Dim] T cells but not on [Gamma][[Delta].sup.Bright] IELs. Thus, treatment of [Gamma][[Delta].sup.Dim] T cells with rmIL-2 and rmIL-7 resulted in high proliferative responses, whereas [Gamma][[Delta].sup.Bright] T cells did not respond to these two cytokines. The sources of these two cytokines for [Gamma][[Delta].sup.Dim] T cells were neighboring epithelial cells (IL-7) and [Alpha][Beta] IELs (IL-2 and IL-7). Cytokine signaling by IL-2 and IL-7 from [Alpha][Beta] T cells and epithelial cells was necessary for the expression of IL-7R and IL-2R, respectively, on a subset of [Gamma][Delta] T cells (e.g., [Gamma][[Delta].sup.Dim] T cells) in mucosa-associated tissue for subsequent activation and cell division.

Fyn is a protein tyrosine kinase that controls the progression of cytokinesis in B lymphocyte progenitor (pro B) cells. Fyn is present in the midspace of dividing pro B cells, at anaphase. The cytokinesis of fyn(-) pro B cells decreases under a serum containing culture condition. The serum-free condition blocks the fyn(-) pro B cell entry into the late telophase. Details of a study conducted on pro B cells from various strains of mice, in a serum-free and chemically defined culture condition, are given.

The transcription factor Eomes/Tbr2 is quickly expressed in the embryonic subventricular zone (SVZ) which is main region for generating cortical projection neurons. A number of crucial functions for Tbr2 as a chief regulator of cortical neurogenesis in the SVZ are discussed.

Author(s): Igor M. Samokhvalov (corresponding author) [1]; Natalia I. Samokhvalova [1]; Shin-ichi Nishikawa [1] Early studies seemed to indicate that in the mammalian embryo, HSCs originate in the yolk sac [...]