The fate of pluripotent stem cells is tightly controlled during early embryonic development. Both the derivation and the maintenance of embryonic stem cells (ES cells) in vitro depend on feeder cell-derived growth factors that are largely unidentified. To dissect the mechanisms governing pluripotency, we conducted a screen to identify factors that are produced by mouse embryonic fibroblast STO cells and are required to maintain the pluripotency of ES cells. One of the factors is bone morphogenetic protein 4 (BMP4). Unexpectedly, the major effect of BMP4 on the self-renewal of ES cells is accomplished by means of the inhibition of both extracellular receptor kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) pathways, and inhibitors of ERK and p38 MAPKs mimic the effect of BMP4 on ES cells. Importantly, inhibition of the p38 MAPK pathway by SB203580 overcomes the block in deriving ES cells from blastocysts lacking a functional Alk3, the BMP type IA receptor. These results uncover a paradigm for BMP signaling in the biology of pluripotent stem cells.E mbryonic stem cells (ES cells) are able to form all cell types of the body by following normal embryogenesis (1-3). The pluripotency of ES cells has attracted great attention for their potential use in tissue and cell therapy. However, the molecular and developmental mechanisms controlling pluripotency and differentiation of ES cells are largely unknown, and only a very limited number of genes has so far been shown to affect the fate decisions of inner cell mass (ICM) or ES cells. These genes include Oct4, Fgf4, H2az, Foxd3, Nanog,.Growth factors required for ES cell self-renewal are usually provided by feeder cells, or exogenously (13). Leukemiainhibiting factor (LIF) and its close relatives are the known propluripotency factors for mouse ES cells. It is unclear how many other growth factors or signaling pathways are required for the self-renewal of ES cells. To address these questions, we set out to identify such factors that affect the self-renewal of ES cells. To accomplish this, we isolated and screened sublines of the mouse embryonic fibroblast STO cells for their ability to support the self-renewal of ES cells by using Oct4-GFP as a convenient marker of pluripotency (14-16). By this approach in combination with gene expression profiling, we have identified bone morphogenetic protein 4 (BMP4) as part of the extracellular propluripotency cues. Also, our studies show that BMP4 and LIF have synergistic effect in teratoma formation. Moreover, a number of genes differentially expressed in ES cells cultured with or without exogenous BMP4 have been identified.One of these differentially expressed genes, X-linked inhibitor of apoptosis (Xiap), is expressed at higher levels in ES cells cultured in the presence of exogenous BMP4 than in its absence. XIAP has been implicated in connecting the type I receptors of BMPs and TGF-␤s with the mitogen-activated protein kinase (MAPK) p38 pathway (17)(18)(19)(20). Contrary to previous findings in which BMP signaling up-r...

Embryonic stem (ES) cells rely on growth factors provided by feeder cells or exogenously to maintain their pluripotency. In order to identify such factors, we have established sub-lines of STO feeder cells which exhibit variable ability in supporting ES cell self-renewal. Functional screening identifies WNT5A and WNT6 as STO cell-produced factors that potently inhibit ES cell differentiation in a serum-dependent manner. Furthermore, direct activation of beta-catenin without disturbing the upstream components of the WNT/beta-catenin pathway fully recapitulates the effect of WNTs on ES cells. Importantly, the WNT/beta-catenin pathway up-regulates the mRNA for Stat3, a known regulator of ES cell self-renewal in the mouse. Finally, LIF is able to mimic the serum effect to act synergistically with WNT proteins to inhibit ES cell differentiation. Therefore, our study reveals part of the molecular mechanisms by which the WNT/beta-catenin pathway acts to prevent ES cell differentiation through convergence on the LIF/JAK-STAT pathway at the level of STAT3.

The spermatogenesis and oogenesis-specific transcription factor Sohlh2 is normally expressed only in premeiotic germ cells. In this study, Sohlh2 and several other germ cell transcripts were found to be induced in mouse embryonic stem cells when cultured on a feeder cell line that overexpresses bone morphogenetic protein 4. To study the function of Sohlh2 in germ cells, we generated mice harboring null alleles of Sohlh2. Male Sohlh2-deficient mice were infertile because of a block in spermatogenesis. Although normal prior to birth, Sohlh2-null mice had reduced numbers of intermediate and type B spermatogonia by postnatal day 7. By day 10, development to the preleptotene spermatocyte stage was severely disrupted, rendering seminiferous tubules with only Sertoli cells, undifferentiated spermatogonia, and degenerating colonies of differentiating spermatogonia. Degenerating cells resembled type A2 spermatogonia and accumulated in M-phase prior to death. A similar phenotype was observed in Sohlh2-null mice on postnatal days 14, 21, 35, 49, 68, and 151. In adult Sohlh2-mutant mice, the ratio of undifferentiated type A spermatogonia (DAZL؉/ PLZF؉) to differentiating type A spermatogonia (DAZL؉/ PLZF؊) was twice normal levels. In culture, undifferentiated type A spermatogonia isolated from Sohlh2-null mice proliferated normally but linked the mutant phenotype to aberrant cell surface expression of the receptor-tyrosine kinase cKit. Thus, Sohlh2 is required for progression of differentiating type A spermatogonia into type B spermatogonia. One conclusion originating from these studies would be that testicular factors normally regulate the viability of differentiating spermatogonia by signaling through Sohlh2. This regulation would provide a crucial checkpoint to optimize the numbers of spermatocytes entering meiosis during each cycle of spermatogenesis. STEM CELLS 2008;26: 1587-1597 Disclosure of potential conflicts of interest is found at the end of this article.

Alzheimer’s disease (AD) is characterized by the accumulation of β-amyloid peptide (Aβ) and loss of neurons. Recently, a growing body of evidences have indicated that as a herbal compound naturally derived from grapes, resveratrol modulates the pathophysiology of AD, however, with a largely unclear mechanism. Therefore, we aimed to investigate the protection of resveratrol against the neurotoxicity of β-amyloid peptide 25–35 (Aβ25–35) and further explore its underlying mechanism in the present study. PC12 cells were injuried by Aβ25–35, and resveratrol at different concentrations was added into the culture medium. We observed that resveratrol increased cell viability through the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) colorimetric assays. Flow cytometry indicated the reduction of cell apoptosis by resveratrol. Moreover, resveratrol also stabilized the intercellular Ca2+ homeostasis and attenuated Aβ25–35 neurotoxicity. Additionally, Aβ25–35-suppressed silent information regulator 1 (SIRT1) activity was significantly reversed by resveratrol, resulting in the downregulation of Rho-associated kinase 1 (ROCK1). Our results clearly revealed that resveratrol significantly protected PC12 cells and inhibited the β-amyloid-induced cell apoptosis through the upregulation of SIRT1. Moreover, as a downstream signal molecule, ROCK1 was negatively regulated by SIRT1. Taken together, our study demonstrated that SIRT1-ROCK1 pathway played a critical role in the pathomechanism of AD.