Plzf regulates germline progenitor self-renewal by opposing mTORC1

PLZF mediates the PTEN/AKT/FOXO3a signaling in suppression of prostate tumorigenesis

Promyelocytic leukemia zinc finger (PLZF) protein expression is closely related to the progression of human cancers, including prostate cancer (PCa). However, the according context of a signaling pathway for PLZF to suppress prostate tumorigenesis remains greatly unknown. Here we report that PLZF is a downstream mediator of the PTEN signaling pathway in PCa. We found that PLZF expression is closely correlated with PTEN expression in a cohort of prostate cancer specimens. Interestingly, both PTEN rescue and phosphoinositide 3-kinase (PI3K) inhibitor LY294002 treatment increase the PLZF expression in prostate cancer cell lines. Further, luciferase reporter assay and chromatin immunoprecipitation assay demonstrate that FOXO3a, a transcriptional factor phosphorylated by PI3K/AKT, could directly bind to the promoter of PLZF gene. These results indicate that PTEN regulates PLZF expression by AKT/FOXO3a. Moreover, our animal experiments also demonstrate that PLZF is capable of inhibiting prostate tumorigenesis in vivo. Taken together, our study defines a PTEN/PLZF pathway and would shed new lights for developing therapeutic strategy of prostate cancer.

Branched chain amino acid suppresses hepatocellular cancer stem cells through the activation of mammalian target of rapamycin

Differentiation of cancer stem cells (CSCs) into cancer cells causes increased sensitivity to chemotherapeutic agents. Although inhibition of mammalian target of rapamycin (mTOR) leads to CSC survival, the effect of branched chain amino acids (BCAAs), an mTOR complex 1 (mTORC1) activator remains unknown. In this study, we examined the effects of BCAA on hepatocellular carcinoma (HCC) cells expressing a hepatic CSC marker, EpCAM. We examined the effects of BCAA and/or 5-fluorouracil (FU) on expression of EpCAM and other CSC-related markers, as well as cell proliferation in HCC cells and in a xenograft mouse model. We also characterized CSC-related and mTOR signal-related molecule expression and tumorigenicity in HCC cells with knockdown of Rictor or Raptor, or overexpression of constitutively active rheb (caRheb). mTOR signal-related molecule expression was also examined in BCAA-treated HCC cells. In-vitro BCAA reduced the frequency of EpCAM-positive cells and improved sensitivity to the anti-proliferative effect of 5-FU. Combined 5-FU and BCAA provided better antitumor efficacy than 5-FU alone in the xenograft model. Stimulation with high doses of BCAA activated mTORC1. Knockdown and overexpression experiments revealed that inhibition of mTOR complex 2 (mTORC2) or activation of mTORC1 led to decreased EpCAM expression and little or no tumorigenicity. BCAA may enhance the sensitivity to chemotherapy by reducing the population of cscs via the mTOR pathway. This result suggests the utility of BCAA in liver cancer therapy.

Characterization of spermatogonial markers in the mature testis of the dogfish (Scyliorhinus canicula L.)

In dogfish, spermatogenesis progresses from a restricted germinative zone, which lines the dorsal testicular vessel. Single spermatogonia (A(s)), including the spermatogonial stem cells (SSCs), produce successively paired (A(p)), undifferentiated (A(u4) to A(u512)), and differentiated (A(d1) to A(d8)) spermatogonia and preleptotene (PL) spermatocytes through 13 mitoses. Dogfish spermatogonial subpopulations present classical morphological characteristics but cannot be distinguished on the basis of molecular markers. This characterization has been initiated in mammals despite the difficulty to separate each spermatogonial subpopulation. For instance, both glial cell-derived neurotrophic factor family receptor alpha 1 (GFRα1) and promyelocytic leukemia zinc finger protein (PLZF) are markers of undifferentiated spermatogonia, whereas receptor tyrosine kinase C-kit is a marker of differentiated spermatogonia. The aim of this study is to characterize spermatogonial markers and to differentiate several spermatogonial subpopulations. Dogfish cDNA sequences have been identified and validated by phylogenetic analyses for gfrα1, plzf, pou2, as well as for high-mobility group box proteins 2 and 3 (hmgb2 and 3) and for mini-chromosome maintenance protein 6 (mcm6). We have used the anatomical advantage of the polarized dogfish testis to analyze the expression of those markers by RT-PCR and in situ hybridization. gfrα1, pou2, and plzf have been detected in the testicular germinative zone, suggesting that spermatogonial markers are relatively well conserved among vertebrates but with a less restricted expression for plzf. Moreover, hmgb3 and mcm6 have been identified as new markers of differentiated spermatogonia. Finally, this first molecular characterization of spermatogonial subpopulations in a chondrichthyan model will be useful for further studies on the SSC niche evolution.

PLZF regulates fibroblast growth factor responsiveness and maintenance of neural progenitors

A transcription factor called Promyelocytic Leukemia Zinc Finger (PLZF) calibrates the balance between spinal cord progenitor maintenance and differentiation by enhancing their sensitivity to mitogens that are present in developing embryos.

Distinct classes of neurons and glial cells in the developing spinal cord arise at specific times and in specific quantities from spatially discrete neural progenitor domains. Thus, adjacent domains can exhibit marked differences in their proliferative potential and timing of differentiation. However, remarkably little is known about the mechanisms that account for this regional control. Here, we show that the transcription factor Promyelocytic Leukemia Zinc Finger (PLZF) plays a critical role shaping patterns of neuronal differentiation by gating the expression of Fibroblast Growth Factor (FGF) Receptor 3 and responsiveness of progenitors to FGFs. PLZF elevation increases FGFR3 expression and STAT3 pathway activity, suppresses neurogenesis, and biases progenitors towards glial cell production. In contrast, PLZF loss reduces FGFR3 levels, leading to premature neuronal differentiation. Together, these findings reveal a novel transcriptional strategy for spatially tuning the responsiveness of distinct neural progenitor groups to broadly distributed mitogenic signals in the embryonic environment.

The embryonic spinal cord is organized into an array of discrete neural progenitor domains along the dorsoventral axis. Most of these domains undergo two periods of differentiation, first producing specific classes of neurons and then generating distinct populations of glial cells at later times. In addition, each of these progenitors pools exhibit marked differences in their proliferative capacities and propensity to differentiate to produce the appropriate numbers and diversity of neurons and glia needed to form functional neural circuits. The mechanisms behind this regional control of neural progenitor behavior, however, remain unclear. In this study, we identify the transcription factor Promyelocytic Leukemia Zinc Finger (PLZF) as a critical regulator of this process in the chick spinal cord. We show that PLZF is initially expressed by all spinal cord progenitors and then becomes restricted to a central domain, where it helps to limit the rate of neuronal differentiation and to preserve the progenitor pool for subsequent glial production. We also demonstrate that PLZF acts by promoting the expression of Fibroblast Growth Factor (FGF) Receptor 3, thereby enhancing the proliferative response of neural progenitors to FGFs present in developing embryos. Together, these findings reveal a novel developmental strategy for spatially controlling neural progenitor behavior by tuning their responsiveness to broadly distributed growth-promoting signals in the embryonic environment.

The RNA binding protein ESRP1 fine-tunes the expression of pluripotency-related factors in mouse embryonic stem cells

In pluripotent stem cells, there is increasing evidence for crosstalk between post-transcriptional and transcriptional networks, offering multifold steps at which pluripotency can be controlled. In addition to well-studied transcription factors, chromatin modifiers and miRNAs, RNA-binding proteins are emerging as fundamental players in pluripotency regulation. Here, we report a new role for the RNA-binding protein ESRP1 in the control of pluripotency. Knockdown of Esrp1 in mouse embryonic stem cells induces, other than the well-documented epithelial to mesenchymal-like state, also an increase in expression of the core transcription factors Oct4, Nanog and Sox2, thereby enhancing self-renewal of these cells. Esrp1-depleted embryonic stem cells displayed impaired early differentiation in vitro and formed larger teratomas in vivo when compared to control embryonic stem cells. We also show that ESRP1 binds to Oct4 and Sox2 mRNAs and decreases their polysomal loading. ESRP1 thus acts as a physiological regulator of the finely-tuned balance between self-renewal and commitment to a restricted developmental fate. Importantly, both mouse and human epithelial stem cells highly express ESRP1, pinpointing the importance of this RNA-binding protein in stem cell biology.

THY1 as a reliable marker for enrichment of undifferentiated spermatogonia in the goat

Spermatogonial stem cells are unique cells of testes that can restore fertility upon transplantation into recipient testes. However, use of suitable markers for enrichment of these cells have important potential application. THY1, is an established conserved marker of spermatogonial stem cells in bovine, rodents, and primates, but there is no information available in goats. After three rounds of enzymatic digestion of prepubertal goat testicular tissues, undifferentiated spermatogonia positive for THY1 were isolated by magnetic-activated cell sorting and were used for immunocytochemistry, real-time polymerase chain reaction analysis for gene expression, protein expression, and transplantation into recipient mice. Immunocytochemical analyses showed that significantly higher percentage of THY1(+) cells were positive for PLZF and VASA when compared with unselected population. This result for PLZF was further confirmed at the protein level. Real-time polymerase chain reaction analysis revealed that expression of THY1, PLZF, VASA, BCL6B, and UCHL1 as SCCs characteristic genes in THY1(+) cells was significantly higher than in the initial population. Finally, transplantation of PKH26-labeled cells revealed that THY1(+) cells had higher capacity for colony formation when compared with unselected cells. In conclusion, the results provide indications that THY1 surface marker can be reliably used for enrichment of undifferentiated spermatogonial in the goats.

mTOR signaling in neural stem cells: from basic biology to disease

The mammalian target of rapamycin (mTOR) pathway is a central controller of growth and homeostasis, and, as such, is implicated in disease states where growth is deregulated, namely cancer, metabolic diseases, and hamartoma syndromes like tuberous sclerosis complex (TSC). Accordingly, mTOR is also a pivotal regulator of the homeostasis of several distinct stem cell pools in which it finely tunes the balance between stem cell self-renewal and differentiation. mTOR hyperactivation in neural stem cells (NSCs) has been etiologically linked to the development of TSC-associated neurological lesions, such as brain hamartomas and benign tumors. Animal models generated by deletion of mTOR upstream regulators in different types of NSCs reproduce faithfully some of the TSC neurological alterations. Thus, mTOR dysregulation in NSCs seems to be responsible for the derangement of their homeostasis, thus leading to TSC development. Here we review recent advances in the molecular dissection of the mTOR cascade, its involvement in the maintenance of stem cell compartments, and in particular the implications of mTOR hyperactivation in NSCs in vivo and in vitro.

Transcriptional analysis of histone deacetylase family members reveal similarities between differentiating and aging spermatogonial stem cells

The differentiation of adult stem cells involves extensive chromatin remodeling, mediated in part by the gene products of histone deacetylase (HDAC) family members. While the transcriptional downregulation of HDACs can impede stem cell self-renewal in certain contexts, it may also promote stem cell maintenance under other circumstances. In self-renewing, differentiating, and aging spermatogonial stem cells (SSCs), the gene expression dynamics of HDACs have not yet been characterized. To gain further insight with these studies, we analyzed the transcriptional profiles of six HDAC family members, previously identified to be the most highly expressed in self-renewing SSCs, during stem cell differentiation and aging. Here we discovered that in both differentiating and aging SSCs the expression of Sirt4 increases, while the expression of Hdac2, Hdac6, and Sirt1 decreases. When SSCs are exposed to the lifespan-enhancing drug rapamycin in vivo, the resultant HDAC gene expression patterns are opposite of those seen in the differentiating and aging SSCs, with increased Hdac2, Hdac6, and Sirt1 and decreased Hdac8, Hdac9, and Sirt4. Our findings suggest that HDACs important for stem cell maintenance and oxidative capacity are downregulated as adult stem cells differentiate or age. These results provide important insights into the epigenetic regulation of stem cell differentiation and aging in mammals.

Molecular circuit involving KLK4 integrates androgen and mTOR signaling in prostate cancer

The androgen receptor (AR) and the phosphoinositide 3-kinase (PI3K)/protein kinase B/mammalian target of rapamycin (mTOR) signaling are two of the major proliferative pathways in a number of tissues and are the main therapeutic targets in various disorders, including prostate cancer (PCa). Previous work has shown that there is reciprocal feedback regulation of PI3K and AR signaling in PCa, suggesting that cotargeting both pathways may enhance therapeutic efficacy. Here we show that proteins encoded by two androgen-regulated genes, kallikrein related peptidase 4 (KLK4) and promyelocytic leukemia zinc finger (PLZF), integrate optimal functioning of AR and mTOR signaling in PCa cells. KLK4 interacts with PLZF and decreases its stability. PLZF in turn interacts with AR and inhibits its function as a transcription factor. PLZF also activates expression of regulated in development and DNA damage responses 1, an inhibitor of mTORC1. Thus, a unique molecular switch is generated that regulates both AR and PI3K signaling. Consistently, KLK4 knockdown results in a significant decline in PCa cell proliferation in vitro and in vivo, decreases anchorage-independent growth, induces apoptosis, and dramatically sensitizes PCa cells to apoptosis-inducing agents. Furthermore, in vivo nanoliposomal KLK4 siRNA delivery in mice bearing PCa tumors results in profound remission. These results demonstrate that the activities of AR and mTOR pathways are maintained by KLK4, which may thus be a viable target for therapy.

Direct renin inhibition prevents cardiac dysfunction in a diabetic mouse model: comparison with an angiotensin receptor antagonist and angiotensin-converting enzyme inhibitor

Hyperglycaemia up-regulates intracellular AngII (angiotensin II) production in cardiac myocytes, effects of which are blocked more effectively by renin inhibition than ARBs (angiotensin receptor blockers) or ACEis (angiotensin-converting enzyme inhibitors). In the present study, we determined whether renin inhibition is more effective at preventing diabetic cardiomyopathy than an ARB or ACEi. Diabetes was induced in adult mice for 10 weeks by STZ (streptozotocin). Diabetic mice were treated with insulin, aliskiren (a renin inhibitor), benazeprilat (an ACEi) or valsartan (an ARB) via subcutaneous mini-pumps. Significant impairment in diastolic and systolic cardiac functions was observed in diabetic mice, which was completely prevented by all three RAS (renin-angiotensin system) inhibitors. Hyperglycaemia significantly increased cardiac oxidative stress and circulating inflammatory cytokines, which were blocked by aliskiren and benazeprilat, whereas valsartan was partially effective. Diabetes increased cardiac PRR (prorenin receptor) expression and nuclear translocation of PLZF (promyelocytic zinc finger protein), which was completely prevented by aliskiren and valsartan, and partially by benazeprilat. Renin inhibition provided similar protection of cardiac function to ARBs and ACEis. Activation of PLZF by PRR represented a novel mechanism in diabetic cardiomyopathy. Differential effects of the three agents on oxidative stress, cytokines and PRR expression suggested subtle differences in their mechanisms of action.

Serial enrichment of spermatogonial stem and progenitor cells (SSCs) in culture for derivation of long-term adult mouse SSC lines

Spermatogonial stem and progenitor cells (SSCs) of the testis represent a classic example of adult mammalian stem cells and preserve fertility for nearly the lifetime of the animal. While the precise mechanisms that govern self-renewal and differentiation in vivo are challenging to study, various systems have been developed previously to propagate murine SSCs in vitro using a combination of specialized culture media and feeder cells(1-3). Most in vitro forays into the biology of SSCs have derived cell lines from neonates, possibly due to the difficulty in obtaining adult cell lines(4). However, the testis continues to mature up until ~5 weeks of age in most mouse strains. In the early post-natal period, dramatic changes occur in the architecture of the testis and in the biology of both somatic and spermatogenic cells, including alterations in expression levels of numerous stem cell-related genes. Therefore, neonatally-derived SSC lines may not fully recapitulate the biology of adult SSCs that persist after the adult testis has reached a steady state. Several factors have hindered the production of adult SSC lines historically. First, the proportion of functional stem cells may decrease during adulthood, either due to intrinsic or extrinsic factors(5,6). Furthermore, as with other adult stem cells, it has been difficult to enrich SSCs sufficiently from total adult testicular cells without using a combination of immunoselection or other sorting strategies(7). Commonly employed strategies include the use of cryptorchid mice as a source of donor cells due to a higher ratio of stem cells to other cell types(8). Based on the hypothesis that removal of somatic cells from the initial culture disrupts interactions with the stem cell niche that are essential for SSC survival, we previously developed methods to derive adult lines that do not require immunoselection or cryptorchid donors but rather employ serial enrichment of SSCs in culture, referred to hereafter as SESC(2,3). The method described below entails a simple procedure for deriving adult SSC lines by dissociating adult donor seminiferous tubules, followed by plating of cells on feeders comprised of a testicular stromal cell line (JK1)(3). Through serial passaging, strongly adherent, contaminating non-germ cells are depleted from the culture with concomitant enrichment of SSCs. Cultures produced in this manner contain a mixture of spermatogonia at different stages of differentiation, which contain SSCs, based on long-term self renewal capability. The crux of the SESC method is that it enables SSCs to make the difficult transition from self-renewal in vivo to long-term self-renewal in vitro in a radically different microenvironment, produces long-term SSC lines, free of contaminating somatic cells, and thereby enables subsequent experimental manipulation of SSCs.

Identification of a novel promyelocytic leukemia zinc-finger isoform required for colorectal cancer cell growth and survival

Promyelocytic leukemia zinc-finger (PLZF) is a transcriptional repressor that regulates proliferation, differentiation and apoptosis among various cellular origins. PLZF expression is upregulated in colorectal cancer cell lines but its putative functional role in this context is unknown. Here, we report the identification of a novel p65 PLZF isoform that results from the usage of an evolutionarily conserved alternative translational initiation site. This isoform is devoid of the classical BTB/POZ domain required for nuclear localization and transcriptional repression. Depletion of p65 PLZF expression in colorectal cancer cell lines results in reduction of cell growth, loss of cell anchorage and increase in cell apoptosis. Overall, these results indicate that p65 PLZF is crucial to maintain colorectal cancer cell adhesion as well as survival and must occur independently of the traditionally viewed transcriptional role of PLZF in the course of these biological processes.

Role of LRF/Pokemon in lineage fate decisions

In the human genome, 43 different genes are found that encode proteins belonging to the family of the POK (poxvirus and zinc finger and Krüppel)/ZBTB (zinc finger and broad complex, tramtrack, and bric à brac) factors. Generally considered transcriptional repressors, several of these genes play fundamental roles in cell lineage fate decision in various tissues, programming specific tasks throughout the life of the organism. Here, we focus on functions of leukemia/lymphoma-related factor/POK erythroid myeloid ontogenic factor, which is probably one of the most exciting and yet enigmatic members of the POK/ZBTB family.

MicroRNA 146 (Mir146) modulates spermatogonial differentiation by retinoic acid in mice

Impaired biogenesis of microRNAs disrupts spermatogenesis and leads to infertility in male mice. Spermatogonial differentiation is a key step in spermatogenesis, yet the mechanisms that control this event remain poorly defined. In this study, we discovered microRNA 146 (Mir146) to be highly regulated during spermatogonial differentiation, a process dependent on retinoic acid (RA) signaling. Mir146 transcript levels were diminished nearly 180-fold in differentiating spermatogonia when compared with undifferentiated spermatogonia. Luciferase assays revealed the direct binding of Mir146 to the 3' untranslated region of the mediator complex subunit 1 (Med1), a coregulator of retinoid receptors (RARs and RXRs). Overexpression of Mir146 in cultured undifferentiated spermatogonia reduced Med1 transcript levels, as well as those of differentiation marker kit oncogene (Kit). MED1 protein was also diminished. Conversely, inhibition of Mir146 increased the levels of Kit. When undifferentiated spermatogonia were exposed to RA, Mir146 was downregulated along with a marker for undifferentiated germ cells, zinc finger and BTB domain containing 16 (Zbtb16; Plzf); Kit was upregulated. Overexpression of Mir146 in RA-treated spermatogonia inhibited the upregulation of Kit, stimulated by retinoic acid gene 8 (Stra8), and spermatogenesis- and oogenesis-specific basic helix-loop-helix 2 (Sohlh2). Inhibition of Mir146 in RA-treated spermatogonia greatly enhanced the upregulation of these genes. We conclude that Mir146 modulates the effects of RA on spermatogonial differentiation.

Propagation of adult SSCs: from mouse to human

Adult spermatogonial stem cells (SSCs) represent a distinctive source of stem cells in mammals for several reasons. First, by giving rise to spermatogenesis, SSCs are responsible for the propagation of a father's genetic material. As such, autologous SSCs have been considered for treatment of infertility and other purposes, including correction of inherited disorders. Second, adult spermatogonia can spontaneously produce embryonic-like stem cells in vitro, which could be used as an alternative for therapeutic, diagnostic, or drug discovery strategies for humans. Therefore, an increasing urgency is driving efforts to understand the biology of SSCs and improve techniques to manipulate them in vitro as a prerequisite to achieve the aforementioned goals. The characterization of adult SSCs also requires reproducible methods to isolate and maintain them in long-term culture. Herein, we describe recent major advances and challenges in propagation of adult SSCs from mice and humans during the past few years, including the use of unique cell surface markers and defined cultured conditions.

Gene expression profiling revealed specific spermatogonial stem cell genes in mouse

Mammalian spermatogenesis originates from spermatogonial stem cells (SSCs), which undergo mitosis, meiosis and spermiogenesis in order to generate mature spermatozoa. SSCs are adult stem cells that can both self-renew and differentiate. To maintain pluripotency, SSCs are regulated by both extrinsic factors secreted from surrounding somatic cells and intrinsic factors including specific gene expression programs. Using fluorescent labeled germ line stem cells, mouse gonocytes and SSCs were purified up to 97% by improved FACS method. Through microarray analyses, global gene expression profiles of gonocytes, SSCs, and differentiated cells were compared. A large number of distinctive genes were found to be enriched in respective cell populations, indicating different functional requirements of each cell type. Functional clustering analyses revealed that while gonocytes and SSCs preferentially express genes implicated in gene expression regulation and epigenetic modifications, differentiated cells including somatic cells are enriched with genes encoding proteins involved in various cellular activities. Further in situ hybridization and RT-PCR experiments confirmed SSC specific expression of several genes of which functions have not been characterized in SSCs. The comparative gene expression profiling provides a useful resource for gene discovery in relation to SSC regulation and opens new avenues for the study of molecular mechanisms underlying SSC self-renewal and differentiation.

Germline stem cells: origin and destiny

Germline stem cells are key to genome transmission to future generations. Over recent years, there have been numerous insights into the regulatory mechanisms that govern both germ cell specification and the maintenance of the germline in adults. Complex regulatory interactions with both the niche and the environment modulate germline stem cell function. This perspective highlights some examples of this regulation to illustrate the diversity and complexity of the mechanisms involved.

Rapamycin increases oxidative stress response gene expression in adult stem cells

Balancing quiescence with proliferation is of paramount importance for adult stem cells in order to avoid hyperproliferation and cell depletion. In some models, stem cell exhaustion may be reversed with the drug rapamycin, which was shown can suppress cellular senescence in vitro and extend lifespan in animals. We hypothesized that rapamycin increases the expression of oxidative stress response genes in adult stem cells, and that these gene activities diminish with age. To test our hypothesis, we exposed mice to rapamycin and then examined the transcriptome of their spermatogonial stem cells (SSCs). Gene expression microarray analysis revealed that numerous oxidative stress response genes were upregulated upon rapamycin treatment, including superoxide dismutase 1, glutathione reductase, and delta-aminolevulinate dehydratase. When we examined the expression of these genes in 55-week-old wild type SSCs, their levels were significantly reduced compared to 3-week-old SSCs, suggesting that their downregulation is coincident with the aging process in adult stem cells. We conclude that rapamycin-induced stimulation of oxidative stress response genes may promote cellular longevity in SSCs, while a decline in gene expression in aged stem cells could reflect the SSCs' diminished potential to alleviate oxidative stress, a hallmark of aging.

Spermatogonial stem cell markers and niche in equids

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis and are located in a highly dynamic microenvironment called "niche" that influences all aspects of stem cell function, including homing, self-renewal and differentiation. Several studies have recently identified specific proteins that regulate the fate of SSCs. These studies also aimed at identifying surface markers that would facilitate the isolation of these cells in different vertebrate species. The present study is the first to investigate SSC physiology and niche in stallions and to offer a comparative evaluation of undifferentiated type A spermatogonia (Aund) markers (GFRA1, PLZF and CSF1R) in three different domestic equid species (stallions, donkeys, and mules). Aund were first characterized according to their morphology and expression of the GFRA1 receptor. Our findings strongly suggest that in stallions these cells were preferentially located in the areas facing the interstitium, particularly those nearby blood vessels. This distribution is similar to what has been observed in other vertebrate species. In addition, all three Aund markers were expressed in the equid species evaluated in this study. These markers have been well characterized in other mammalian species, which suggests that the molecular mechanisms that maintain the niche and Aund/SSCs physiology are conserved among mammals. We hope that our findings will help future studies needing isolation and cryopreservation of equids SSCs. In addition, our data will be very useful for studies that aim at preserving the germplasm of valuable animals, and involve germ cell transplantation or xenografts of equids testis fragments/germ cells suspensions.

Direct differentiation of human pluripotent stem cells into haploid spermatogenic cells

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.

The BTB-ZF transcription factors

The BTB-ZF (broad-complex, tramtrack and bric-à-brac--zinc finger) proteins are encoded by at least 49 genes in mouse and man and commonly serve as sequence-specific silencers of gene expression. This review will focus on the known physiological functions of mammalian BTB-ZF proteins, which include essential roles in the development of the immune system. We discuss their function in terminally differentiated lymphocytes and the progenitors that give rise to them, their action in hematopoietic malignancy and roles beyond the immune system.

Functional antagonism between Sall4 and Plzf defines germline progenitors

Transcription factors required for formation of embryonic tissues often maintain their expression in adult stem cell populations, but whether their function remains equivalent is not clear. Here we demonstrate critical and distinct roles for Sall4 in development of embryonic germ cells and differentiation of postnatal spermatogonial progenitor cells (SPCs). In differentiating SPCs, Sall4 levels transiently increase and Sall4 physically interacts with Plzf, a transcription factor exclusively required for adult stem cell maintenance. Mechanistically, Sall4 sequesters Plzf to noncognate chromatin domains to induce expression of Kit, a target of Plzf-mediated repression required for differentiation. Plzf in turn antagonizes Sall4 function by displacing Sall4 from cognate chromatin to induce Sall1 expression. Taken together, these data suggest that transcription factors required for embryonic tissue development postnatally take on distinct roles through interaction with opposing factors, which hence define properties of the adult stem cell compartment.

Nuclear factor of activated T-cell c3 inhibition of mammalian target of rapamycin signaling through induction of regulated in development and DNA damage response 1 in human intestinal cells

Our results demonstrate that nuclear factor of activated T-cell 3 (NFATc3) contributes to the regulation of the mammalian target of rapamycin (mTOR) repressor regulated in development and DNA damage response 1 (REDD1) and mTOR downstream-targeted c-Myc expression. Furthermore, our study demonstrates a novel role for the NFATc3/REDD1/tuberous sclerosis complex 2 axis in the regulation of goblet cell differentiation.

The nuclear factor of activated T-cell (NFAT) proteins are a family of transcription factors (NFATc1–c4) involved in the regulation of cell differentiation. We identified REDD1, a negative regulator of mammalian target of rapamycin (mTOR) through the tuberous sclerosis complex (TSC1/2 complex), as a new molecular target of NFATc3. We show that treatment with a combination of phorbol 12-myristate 13-acetate (PMA) plus ionophore A23187 (Io), which induces NFAT activation, increased REDD1 mRNA and protein expression and inhibited mTOR signaling; pretreatment with the calcineurin inhibitor cyclosporin A (CsA), an antagonist of NFAT signaling, decreased REDD1 induction and mTOR inhibition. Knockdown of NFATc3, not NFATc1, NFATc2, or NFATc4, attenuated PMA/Io-induced REDD1 expression. Treatment with PMA/Io increased REDD1 promoter activity and increased NFATc3 binding to the REDD1 promoter. Overexpression of NFATc3 increased REDD1 mRNA and protein expression and increased PMA/Io-mediated REDD1 promoter activity. Treatment with PMA/Io increased expression of the goblet cell differentiation marker MUC2; these changes were attenuated by pretreatment with CsA or knockdown of REDD1 or NFATc3. Overexpression of NFATc3 increased, while knockdown of TSC2 decreased, MUC2 expression. We provide evidence showing NFATc3 inhibits mTOR via induction of REDD1. Our results suggest a role for the NFATc3/REDD1/TSC2 axis in the regulation of intestinal cell differentiation.

POK/ZBTB proteins: an emerging family of proteins that regulate lymphoid development and function

The germinal center (GC) is a unique histological structure found in peripheral lymphoid organs. GCs provide an important source of humoral immunity by generating high affinity antibodies against a pathogen. The GC response is tightly regulated during clonal expansion, immunoglobulin modification, and affinity maturation, whereas its deregulation has a detrimental effect on immune function, leading to development of diseases, such as lymphoma and autoimmunity. LRF (lymphoma/leukemia-related factor), encoded by the ZBTB7A gene, is a transcriptional repressor belonging to the POK (POZ and Krüppel)/ZBTB (zing finger and BTB) protein family. LRF was originally identified as a PLZF (promyelocytic leukemia zinc finger) homolog that physically interacts with BCL6 (B-cell lymphoma 6), whose expression is required for GC formation and associated with non-Hodgkin's lymphoma. Recently, our group demonstrated that LRF plays critical roles in regulating lymphoid lineage commitment, mature B-cell development, and the GC response via distinct mechanisms. Herein, we review POK/ZBTB protein function in lymphoid development, with particular emphasis on the role of LRF in GC B cells.

Sustained activation of mTOR pathway in embryonic neural stem cells leads to development of tuberous sclerosis complex-associated lesions

Tuberous Sclerosis Complex (TSC) is a multisystem genetic disorder characterized by hamartomatous neurological lesions that exhibit abnormal cell proliferation and differentiation. Hyperactivation of mTOR pathway by mutations in either the Tsc1 or Tsc2 gene underlies TSC pathogenesis, but involvement of specific neural cell populations in the formation of TSC-associated neurological lesions remains unclear. We deleted Tsc1 in Emx1-expressing embryonic telencephalic neural stem cells (NSCs) and found that mutant mice faithfully recapitulated TSC neuropathological lesions, such as cortical lamination defects and subependymal nodules (SENs). These alterations were caused by enhanced generation of SVZ neural progeny, followed by their premature differentiation and impaired maturation during both embryonic and postnatal development. Notably, mTORC1-dependent Akt inhibition and STAT3 activation were involved in the reduced self-renewal and earlier neuronal and astroglial differentiation of mutant NSCs. Thus, finely tuned mTOR activation in embryonic NSCs may be critical to prevent development of TSC-associated brain lesions.

CIP2A promotes proliferation of spermatogonial progenitor cells and spermatogenesis in mice

Protein phosphatase 2A (PP2A) is a critical regulator of protein serine/threonine phosphorylation. However, the physiological and developmental roles of different PP2A complexes are very poorly understood. Here, we show that a newly characterized PP2A inhibitory protein CIP2A is co-expressed with ki-67 and with self-renewal protein PLZF in the spermatogonial progenitor cell (SPC) population in the testis. CIP2A and PLZF expression was shown also to correlate Ki-67 expression in human testicular spermatogonia. Functionally, CIP2A mutant mouse testes exhibited smaller number of PLZF-positive SPCs and reduced sperm counts. Moreover, seminiferous tubuli cells isolated from CIP2A mutant mice showed reduced expression of Plzf and other renewal genes Oct-4 and Nanog at mRNA level. However, PLZF-deficient testes did not show altered CIP2A expression. Importantly, spermatogonia-specific restoration of CIP2A expression rescued PLZF expression and sperm production defects observed in CIP2A mutant mice. Taken together, these results reveal first physiological function for an emerging human oncoprotein CIP2A, and provide insights into maintenance of PLZF-positive progenitors. Moreover, demonstration that CIP2A expression can be systematically inhibited without severe consequences to normal mouse development and viability may have clinical relevance regarding targeting of oncogenic CIP2A for future cancer therapies.

Production of zebrafish offspring from cultured spermatogonial stem cells

Germ-line stem cells have the potential to be a very powerful tool for modifying the genetic information of individual animals. As a first step to use spermatogonial stem cells (SSCs) to enable genetic modification, we here describe effective long-term culture conditions for propagating zebrafish SSCs and for the production of offspring from these cultured SSCs after their differentiation into sperm in transplanted testicular cell aggregates. Dissociated testicular cells were cultured in specific medium with some modified supplements, including several mammalian growth factors. The spermatogonia actively proliferated and retained the expression of exogenous green fluorescent protein under the control of vas and sox17 promoters and also of promyelocytic leukemia zinc finger (Plzf), a marker of undifferentiated spermatogonia, after 1 month in culture. This is a longer period than the entire natural spermatogenic cycle (from SSCs to sperm). The use of subcutaneously grafted aggregates of these cultured spermatogonia and freshly dissociated testicular cells showed that these SSCs could undergo self-renewal and differentiation into sperm. Artificial insemination of these grafted aggregates successfully produced offspring. This culture method will facilitate the identification of new factors for the maintenance of SSCs and enable the future enrichment of genetically modified SSCs that will produce offspring in zebrafish.

Regulation of entry into gametogenesis

Gametogenesis is a fundamental aspect of sexual reproduction in eukaryotes. In the unicellular fungi Saccharomyces cerevisiae (budding yeast) and Schizosaccharomyces pombe (fission yeast), where this developmental programme has been extensively studied, entry into gametogenesis requires the convergence of multiple signals on the promoter of a master regulator. Starvation signals and cellular mating-type information promote the transcription of cell fate inducers, which in turn initiate a transcriptional cascade that propels a unique type of cell division, meiosis, and gamete morphogenesis. Here, we will provide an overview of how entry into gametogenesis is initiated in budding and fission yeast and discuss potential conserved features in the germ cell development of higher eukaryotes.

Molecular control of rodent spermatogenesis

Spermatogenesis is a complex developmental process that ultimately generates mature spermatozoa. This process involves a phase of proliferative expansion, meiosis, and cytodifferentiation. Mouse models have been widely used to study spermatogenesis and have revealed many genes and molecular mechanisms that are crucial in this process. Although meiosis is generally considered as the most crucial phase of spermatogenesis, mouse models have shown that pre-meiotic and post-meiotic phases are equally important. Using knowledge generated from mouse models and in vitro studies, the current review provides an overview of the molecular control of rodent spermatogenesis. Finally, we briefly relate this knowledge to fertility problems in humans and discuss implications for future research. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Mammalian target of rapamycin: a signaling kinase for every aspect of cellular life

The mammalian (or mechanistic) target of rapamycin (mTOR) is an evolutionarily conserved serine-threonine kinase that is known to sense the environmental and cellular nutrition and energy status. Diverse mitogens, growth factors, and nutrients stimulate the activation of the two mTOR complexes mTORC1 and mTORC2 to regulate diverse functions, such as cell growth, proliferation, development, memory, longevity, angiogenesis, autophagy, and innate as well as adaptive immune responses. Dysregulation of the mTOR pathway is frequently observed in various cancers and in genetic disorders, such as tuberous sclerosis complex or cystic kidney disease. In this review, I will give an overview of the current understanding of mTOR signaling and its role in diverse tissues and cells. Genetic deletion of specific mTOR pathway proteins in distinct tissues and cells broadened our understanding of the cell-specific roles of mTORC1 and mTORC2. Inhibition of mTOR is an established therapeutic principle in transplantation medicine and in cancers, such as renal cell carcinoma. Pharmacological targeting of both mTOR complexes by novel drugs potentially expand the clinical applicability and efficacy of mTOR inhibition in various disease settings.

Cyclical and patch-like GDNF distribution along the basal surface of Sertoli cells in mouse and hamster testes

Background and Aims

In mammalian spermatogenesis, glial cell line-derived neurotrophic factor (GDNF) is one of the major Sertoli cell-derived factors which regulates the maintenance of undifferentiated spermatogonia including spermatogonial stem cells (SSCs) through GDNF family receptor α1 (GFRα1). It remains unclear as to when, where and how GDNF molecules are produced and exposed to the GFRα1-positive spermatogonia in vivo.

Methodology and Principal Findings

Here we show the cyclical and patch-like distribution of immunoreactive GDNF-positive signals and their close co-localization with a subpopulation of GFRα1-positive spermatogonia along the basal surface of Sertoli cells in mice and hamsters. Anti-GDNF section immunostaining revealed that GDNF-positive signals are mainly cytoplasmic and observed specifically in the Sertoli cells in a species-specific as well as a seminiferous cycle- and spermatogenic activity-dependent manner. In contrast to the ubiquitous GDNF signals in mouse testes, high levels of its signals were cyclically observed in hamster testes prior to spermiation. Whole-mount anti-GDNF staining of the seminiferous tubules successfully visualized the cyclical and patch-like extracellular distribution of GDNF-positive granular deposits along the basal surface of Sertoli cells in both species. Double-staining of GDNF and GFRα1 demonstrated the close co-localization of GDNF deposits and a subpopulation of GFRα1-positive spermatogonia. In both species, GFRα1-positive cells showed a slender bipolar shape as well as a tendency for increased cell numbers in the GDNF-enriched area, as compared with those in the GDNF-low/negative area of the seminiferous tubules.

Conclusion/Significance

Our data provide direct evidence of regionally defined patch-like GDNF-positive signal site in which GFRα1-positive spermatogonia possibly interact with GDNF in the basal compartment of the seminiferous tubules.

Long glucocorticoid-induced leucine zipper (L-GILZ) protein interacts with ras protein pathway and contributes to spermatogenesis control

Correct function of spermatogonia is critical for the maintenance of spermatogenesis throughout life, but the cellular pathways regulating undifferentiated spermatogonia proliferation, differentiation, and survival are only partially known. We show here that long glucocorticoid-induced leucine zipper (L-GILZ) is highly expressed in spermatogonia and primary spermatocytes and controls spermatogenesis. Gilz deficiency in knock-out (gilz KO) mice leads to a complete loss of germ cell lineage within first cycles of spermatogenesis, resulting in male sterility. Spermatogenesis failure is intrinsic to germ cells and is associated with increased proliferation and aberrant differentiation of undifferentiated spermatogonia and with hyperactivity of Ras signaling pathway as indicated by an increase of ERK and Akt phosphorylation. Spermatogonia differentiation does not proceed beyond the prophase of the first meiotic division due to massive apoptosis associated with accumulation of unrepaired chromosomal damage. These results identify L-GILZ as a novel important factor for undifferentiated spermatogonia function and spermatogenesis.

Germline stem cells

Sperm and egg production requires a robust stem cell system that balances self-renewal with differentiation. Self-renewal at the expense of differentiation can cause tumorigenesis, whereas differentiation at the expense of self-renewal can cause germ cell depletion and infertility. In most organisms, and sometimes in both sexes, germline stem cells (GSCs) often reside in a defined anatomical niche. Factors within the niche regulate a balance between GSC self-renewal and differentiation. Asymmetric division of the germline stem cell to form daughter cells with alternative fates is common. The exception to both these tendencies is the mammalian testis where there does not appear to be an obvious anatomical niche and where GSC homeostasis is likely accomplished by a stochastic balance of self-renewal and differentiation and not by regulated asymmetric cell division. Despite these apparent differences, GSCs in all organisms share many common mechanisms, although not necessarily molecules, to guarantee survival of the germline.

Drosophila stem cell niches: a decade of discovery suggests a unified view of stem cell regulation

The past decade of research on Drosophila stem cells and niches has provided key insights. Fly stem cells do not occupy a special "state" based on novel "stem cell genes" but resemble transiently arrested tissue progenitors. Moreover, individual stem cells and downstream progenitors are highly dynamic and dispensable, not tissue bulwarks. Niches, rather than fixed cell lineages, ensure tissue health by holding stem cells and repressing cell differentiation inside, but not outside. We review the five best-understood adult Drosophila stem cells and argue that the fundamental biology of stem cells and niches is conserved between Drosophila and mice.

Foxo1 is required in mouse spermatogonial stem cells for their maintenance and the initiation of spermatogenesis

Spermatogonial stem cells (SSCs) capable of self-renewal and differentiation are the foundation for spermatogenesis. Although several factors important for these processes have been identified, the fundamental mechanisms regulating SSC self-renewal and differentiation remain unknown. Here, we investigated a role for the Foxo transcription factors in mouse spermatogenesis and found that Foxo1 specifically marks mouse gonocytes and a subset of spermatogonia with stem cell potential. Genetic analyses showed that Foxo1 was required for both SSC homeostasis and the initiation of spermatogenesis. Combined deficiency of Foxo1, Foxo3, and Foxo4 resulted in a severe impairment of SSC self-renewal and a complete block of differentiation, indicating that Foxo3 and Foxo4, although dispensable for male fertility, contribute to SSC function. By conditional inactivation of 3-phosphoinositide-dependent protein kinase 1 (Pdk1) and phosphatase and tensin homolog (Pten) in the male germ line, we found that PI3K signaling regulates Foxo1 stability and subcellular localization, revealing that the Foxos are pivotal effectors of PI3K-Akt signaling in SSCs. We also identified a network of Foxo gene targets--most notably Ret--that rationalized the maintenance of SSCs by the Foxos. These studies demonstrate that Foxo1 expression in the spermatogenic lineage is intimately associated with the stem cell state and revealed what we believe to be novel Foxo-dependent mechanisms underlying SSC self-renewal and differentiation, with implications for common diseases, including male infertility and testicular cancer, due to abnormalities in SSC function.

SPOC1 (PHF13) is required for spermatogonial stem cell differentiation and sustained spermatogenesis

SPOC1 (PHF13) is a recently identified protein that has been shown to dynamically associate with somatic chromatin, to modulate chromatin compaction and to be important for proper cell division. Here, we report on the expression of SPOC1 in promyelocytic leukaemia zinc finger (PLZF)-positive undifferentiated spermatogonial stem cells (SSCs) of the mouse testis. To investigate further the biological function of SPOC1 in germ cells we generated Spoc1 mutant mice from a gene-trap embryonic stem cell clone. Postpubertal homozygous Spoc1(-/-) animals displayed a pronounced progressive loss of germ cells from an initially normal germ epithelium of the testis tubules leading to testis hypoplasia. This loss first affected non-SSC stages of germ cells and then, at a later time point, the undifferentiated spermatogonia. Remarkably, successive loss of all germ cells (at >20 weeks of age) was preceded by a transient increase in the number of undifferentiated A(aligned) (A(al)) spermatogonia in younger mice (at >10 weeks of age). The number of primary Spoc1(-/-) gonocytes, the proliferation of germ cells, and the initiation and progression of meiosis was normal, but we noted a significantly elevated level of apoptosis in the Spoc1(-/-) testis. Taken together, the data argue that SPOC1 is indispensable for stem cell differentiation in the testis and for sustained spermatogenesis.

Spermatogonial stem cell self-renewal requires ETV5-mediated downstream activation of Brachyury in mice

Insight regarding mechanisms controlling gene expression in the spermatogonial stem cell (SSC) will improve our understanding of the processes regulating spermatogenesis and aid in treating problems associated with male infertility. In the present study, we explored the global gene expression profiles of the glial cell line-derived neurotrophic factor (GDNF)-regulated transcription factors Ets (E-twenty-six) variant gene 5 (Etv5); B-cell chronic lymphocytic leukemia (CLL)/lymphoma 6, member B (Bcl6b); and POU domain, class-3 transcription factor 1 (Pou3f1). We reasoned that these three factors may function as a core set of transcription factors, regulating genes responsible for maintaining the SSC population. Using transient siRNA oligonucleotides to individually target Etv5, Bcl6b, and Pou3f1 within mouse SSC cultures, we examined changes to the global gene expression profiles associated with these transcription factors. Only modest overlaps in the target genes regulated by the three factors were noted, but ETV5 was found to be a critical downstream regulator of GDNF signaling that mediated the expression of several known SSC self-renewal related genes, including Bcl6b and LIM homeobox 1 (Lhx1). Notably, ETV5 was identified as a regulator of Brachyury (T) and CXC chemokine receptor, type 4 (Cxcr4), and we showed that ETV5 binding to the Brachyury (T) gene promoter region is associated with an active state of transcription. Moreover, in vivo transplantation of SSCs following silencing of Brachyury (T) significantly reduced the number of donor cell-derived colonies formed within recipient mouse testes. These results suggest Brachyury is of biological importance and functions as part of GDNF/ETV5 signaling to promote self-renewal of mouse SSCs cultured in vitro.

Pluripotency of male germline stem cells

The ethical issues and public concerns regarding the use of embryonic stem (ES) cells in human therapy have motivated considerable research into the generation of pluripotent stem cell lines from non-embryonic sources. Numerous reports have shown that pluripotent cells can be generated and derived from germline stem cells (GSCs) in mouse and human testes during in vitro cultivation. The gene expression patterns of these cells are similar to those of ES cells and show the typical self-renewal and differentiation patterns of pluripotent cells in vivo and in vitro. However, the mechanisms underlying the spontaneous dedifferentiation of GSCs remain to be elucidated. Studies to identify master regulators in this reprogramming process are of critical importance for understanding the gene regulatory networks that sustain the cellular status of these cells. The results of such studies would provide a theoretical background for the practical use of these cells in regenerative medicine. Such studies would also help elucidate the molecular mechanisms underlying certain diseases, such as testicular germ cell tumors.

Hyphal development in Candida albicans requires two temporally linked changes in promoter chromatin for initiation and maintenance

Phenotypic plasticity is common in development. For Candida albicans, the most common cause of invasive fungal infections in humans, morphological plasticity is its defining feature and is critical for its pathogenesis. Unlike other fungal pathogens that exist primarily in either yeast or hyphal forms, C. albicans is able to switch reversibly between yeast and hyphal growth forms in response to environmental cues. Although many regulators have been found involved in hyphal development, the mechanisms of regulating hyphal development and plasticity of dimorphism remain unclear. Here we show that hyphal development involves two sequential regulations of the promoter chromatin of hypha-specific genes. Initiation requires a rapid but temporary disappearance of the Nrg1 transcriptional repressor of hyphal morphogenesis via activation of the cAMP-PKA pathway. Maintenance requires promoter recruitment of Hda1 histone deacetylase under reduced Tor1 (target of rapamycin) signaling. Hda1 deacetylates a subunit of the NuA4 histone acetyltransferase module, leading to eviction of the NuA4 acetyltransferase module and blockage of Nrg1 access to promoters of hypha-specific genes. Promoter recruitment of Hda1 for hyphal maintenance happens only during the period when Nrg1 is gone. The sequential regulation of hyphal development by the activation of the cAMP-PKA pathway and reduced Tor1 signaling provides a molecular mechanism for plasticity of dimorphism and how C. albicans adapts to the varied host environments in pathogenesis. Such temporally linked regulation of promoter chromatin by different signaling pathways provides a unique mechanism for integrating multiple signals during development and cell fate specification.

Many organisms are able to change their phenotype in response to changes in the environment, a phenomenon referred to as plasticity. Candida albicans, a major opportunistic fungal pathogen of humans, can undergo reversible morphological changes between yeast (spherical) and hyphal (filamentous) forms of growth in response to environmental cues. This morphological plasticity is essential for its pathogenesis and survival in its hosts. In this study, we show that hyphal development is initiated and maintained by two major nutrient-sensing cellular growth pathways that act by removing the inhibition provided by the transcriptional repressor Nrg1. While initiation requires a rapid but temporary disappearance of Nrg1 via activation of the cAMP-dependent protein kinase A pathway, maintenance requires the recruitment to promoters of the Hda1 histone deacetylase under conditions of reduced signaling by the target of rapamycin (TOR) kinase, leading to chromatin remodeling that blocks Nrg1 access to the promoters of hypha-specific genes. We observed that recruitment of Hda1 to promoters happens only during the time window when Nrg1 is absent. Such temporally linked regulation of promoter chromatin by different signaling pathways provides a unique mechanism for integrating multiple signals in the regulation of gene expression and phenotypic plasticity during development and cell fate specification.

PW1 gene/paternally expressed gene 3 (PW1/Peg3) identifies multiple adult stem and progenitor cell populations

A variety of markers are invaluable for identifying and purifying stem/progenitor cells. Here we report the generation of a murine reporter line driven by Pw1 that reveals cycling and quiescent progenitor/stem cells in all adult tissues thus far examined, including the intestine, blood, testis, central nervous system, bone, skeletal muscle, and skin. Neurospheres generated from the adult PW1-reporter mouse show near 100% reporter-gene expression following a single passage. Furthermore, epidermal stem cells can be purified solely on the basis of reporter-gene expression. These cells are clonogenic, repopulate the epidermal stem-cell niches, and give rise to new hair follicles. Finally, we demonstrate that only PW1 reporter-expressing epidermal cells give rise to follicles that are capable of self-renewal following injury. Our data demonstrate that PW1 serves as an invaluable marker for competent self-renewing stem cells in a wide array of adult tissues, and the PW1-reporter mouse serves as a tool for rapid stem cell isolation and characterization.

Evaluation of Sycp3, Plzf and Cyclin B3 expression and suitability as spermatogonia and spermatocyte markers in zebrafish

Recent studies in mammals have revealed the heterogeneity of spermatogonial populations which contain differentiated and undifferentiated cells that further divide into actual stem cells and potential stem cells. In fish however, there are no functional definitions, and very few molecular markers, for germ cells. In our present study, specific antibodies were raised against Sycp3, Plzf and Cyclin B3 in zebrafish and then used to determine the localization of these proteins in the testis. We wished to confirm whether these molecules were potential markers for spermatocytes and spermatogonia. Immunohistochemical observations revealed that Sycp3 is specifically localized in spermatocytes in typical nuclear patterns at each meiotic stage. Plzf was found to be localized in the nucleus of both type A and type B spermatogonia until the 8-cell clone, similar to the pattern in Plzf-positive A(single)-A(aligned) undifferentiated spermatogonia in rodents. In addition to Plzf, the localization of Cyclin B3 was predominantly detected in the nuclei of type A and early type B spermatogonia until the 16-cell clone. Additionally, Cyclin B3 protein signals were detected in germ cells in large cysts, possibly corresponding to spermatocytes at the preleptotene stage. Our present data thus show that these molecules have properties that will enable their use as markers of spermatocytes and early spermatogonia in zebrafish.

Understanding PLZF: two transcriptional targets, REDD1 and smooth muscle α-actin, define new questions in growth control, senescence, self-renewal and tumor suppression

PLZF can function as a transcriptional activator or as a transcriptional repressor. Recent studies have identified two direct transcriptional targets of PLZF, REDD1 and smooth muscle α-actin. REDD1 is activated by PLZF. It mediates the PLZF-dependent downregulation of TORC1 and is responsible for the maintenance of pluripotency in cultures of spermatogonial progenitor cells. This activity may extend to other stem-like cell types. The effect of REDD1 on TORC1 also raises the possibility that REDD1 controls cell growth, tumorigenicity and senescence. The regulatory loop extending from PLZF via REDD1 to TORC1 identifies REDD1 as a critical determinant of TOR activity. The transcription of smooth muscle α-actin is repressed by PLZF. In fibroblasts, this downregulation is accompanied by a change of cell shape and a dramatic reorganization of the cytoskeleton. It is also correlated with the acquisition of cellular resistance to oncogenic transformation. The resistance is selective, it works against some oncoproteins but not against others. The molecular mechanisms underlying the changes in the cytoskeleton and in the susceptibility to oncogenic transformation are unknown. However these changes are dependent on the activity of RAS and thus probably involve the RAC/RHO family of proteins.