Developmental gene expression is defined through cross-talk between the function of transcription factors and epigenetic status, including histone modification. Although several transcription factors play crucial roles in mammalian sex determination, how epigenetic regulation contributes to this process remains unknown. We observed male-to-female sex reversal in mice lacking the H3K9 demethylase Jmjd1a and found that Jmjd1a regulates expression of the mammalian Y chromosome sex-determining gene Sry. Jmjd1a directly and positively controls Sry expression by regulating H3K9me2 marks. These studies reveal a pivotal role of histone demethylation in mammalian sex determination.

Transforming growth factor ␤ (TGF-␤) has been implicated in the maintenance of homeostasis in various organs, including the gastric epithelium. In particular, TGF-␤-induced signaling was shown to be required for the differentiation-associated physiological apoptosis of gastric epithelial cells, but its mechanism has not been well understood. In this study, the molecular mechanism of TGF-␤-induced apoptosis was analyzed in a human gastric epithelial cell line, SNU16, as an in vitro model. Expression of Smad7 and Bcl-X L , but not viral FLIP, was shown to prevent TGF-␤-induced apoptosis, indicating an exclusive requirement of the activation of Smad signaling pathway and mitochondrial dysfunction followed by activation of caspase-9. In addition, treatment with TGF-␤ induced binding of Bim, a proapoptotic Bcl-2 homology domain 3 (BH3)-only protein, to Bcl-X L , which is dependent on the activation of Smad, and reduction in the expression of Bim by RNA interference decreased the sensitivity to TGF-␤-induced apoptosis. Moreover, we found abnormalities in the gastric epithelium of both Bim and caspase-9 knockout mice; these abnormalities were associated with a defect of physiological apoptosis in gastric epithelial cells. These results indicate for the first time that TGF-␤ is involved in the physiological loss of gastric epithelial cells by activating apoptosis mediated by Smad, Bim, and caspase-9.Gastric epithelial cells exhibit a rapid rate of turnover, which requires an appropriate balance between the proliferation of progenitor cells and the loss of mature cells (12). Loss of mature epithelial cells at the gastric surface is thought to be mediated mainly by physiological cell death, namely, apoptosis, which always occurs at the surface of the gastrointestinal tract. In the gastric mucosa, 1 to 3% of the epithelial cells were reported to show morphological features of apoptosis at any given time under physiological conditions (47). The physiological loss of gastric epithelial cells is necessary for the maintenance of tissue homeostasis associated with the exchange of mature epithelial cells to fresh proliferating cells, and any defects in this epithelial cell death pathway may be a contributing factor to disease development. However, little direct evidence linking the gastric epithelial cell death and apoptosisrelated molecules has been obtained and the molecular regulation of apoptosis of gastric epithelial cells largely remains unclear. In this study, we focused on transforming growth factor ␤ (TGF-␤) as one of the key regulators in this physiological cell death.TGF-␤ is a multifunctional cytokine, which has essential roles in a variety of physiological or pathological processes (9, 42). While TGF-␤ functions as a potent suppressor of cell proliferation, it can also induce or suppress apoptosis in certain types of cells (39,42). Previous studies have established that the acquisition of resistance to TGF-␤ is a critical step for carcinogenesis in many organs (8). Abnormal expression of TGF-␤ receptors and inactive...

The Y-linked gene Sry regulates mammalian sex determination in bipotential embryonic gonads. Here, we report that the transcription factors Six1 and Six4 are required for male gonadal differentiation. Loss of Six1 and Six4 together, but neither alone, resulted in a male-to-female sex-reversal phenotype in XY mutant gonads accompanied by a failure in Sry activation. Decreased gonadal precursor cell formation at the onset of Sry expression and a gonadal size reduction in both sexes were also found in mutant embryos. Forced Sry transgene expression in XY mutant gonads rescued testicular development but not the initial disruption to precursor growth. Furthermore, we identified two downstream targets of Six1/Six4 in gonadal development, Fog2 (Zfpm2) and Nr5a1 (Ad4BP/Sf1). These two distinct Six1/Six4-regulated pathways are considered to be crucial for gonadal development. The regulation of Fog2 induces Sry expression in male sex determination, and the regulation of Nr5a1 in gonadal precursor formation determines gonadal size.

JmjC domain-containing proteins are a class of enzymes responsible for histone demethylation. Previous studies revealed that the JmjC domain-containing protein KDM3A possesses intrinsic demethylase activity toward lysine 9 of histone H3 and plays essential roles in spermiogenesis. In contrast, the biological roles of JMJD1C, a KDM3A homolog in mice, are largely unknown. Here we present the crucial role of JMJD1C in male gametogenesis. Jmjd1c-deficient males became infertile due to the progressive reduction of germ cells after 3 mo of age. Importantly, Jmjd1c-deficient testes frequently contained abnormal tubules lacking developmentally immature germ cells. JMJD1C is most abundantly expressed in undifferentiated spermatogonia in mouse testis. The numbers of ZBTB16-positive spermatogonia and apoptotic germ cells in Jmjd1c-deficient testes decreased and increased in an age-dependent manner, respectively. Our studies demonstrated that JMJD1C contributes to the long-term maintenance of the male germ line.

SummaryBoth glial cell line-derived neurotrophic factor (GDNF) and fibroblast growth factor 2 (FGF2) are bona fide self-renewal factors for spermatogonial stem cells, whereas retinoic acid (RA) induces spermatogonial differentiation. In this study, we investigated the functional differences between FGF2 and GDNF in the germline niche by providing these factors using a drug delivery system in vivo. Although both factors expanded the GFRA1+ subset of undifferentiated spermatogonia, the FGF2-expanded subset expressed RARG, which is indispensable for proper differentiation, 1.9-fold more frequently than the GDNF-expanded subset, demonstrating that FGF2 expands a differentiation-prone subset in the testis. Moreover, FGF2 acted on the germline niche to suppress RA metabolism and GDNF production, suggesting that FGF2 modifies germline niche functions to be more appropriate for spermatogonial differentiation. These results suggest that FGF2 contributes to induction of differentiation rather than maintenance of undifferentiated spermatogonia, indicating reconsideration of the role of FGF2 in the germline niche.