Distinct PRC2 subunits regulate maintenance and establishment of Polycomb repression during differentiation

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Indian hedgehog signaling from endothelial cells is required for sclera and retinal pigment epithelium development in the mouse eye

The development of extraocular orbital structures, in particular the choroid and sclera, is regulated by a complex series of interactions between neuroectoderm, neural crest and mesoderm derivatives, although in many instances the signals that mediate these interactions are not known. In this study we have investigated the function of Indian hedgehog (Ihh) in the developing mammalian eye. We show that Ihh is expressed in a population of non-pigmented cells located in the developing choroid adjacent to the RPE. The analysis of Hh mutant mice demonstrates that the RPE and developing scleral mesenchyme are direct targets of Ihh signaling and that Ihh is required for the normal pigmentation pattern of the RPE and the condensation of mesenchymal cells to form the sclera. Our findings also indicate that Ihh signals indirectly to promote proliferation and photoreceptor specification in the neural retina. This study identifies Ihh as a novel choroid-derived signal that regulates RPE, sclera and neural retina development.     

Drosophila ESC-like can substitute for ESC and becomes required for Polycomb silencing if ESC is absent

The Drosophila esc-like gene (escl) encodes a protein very similar to ESC. Like ESC, ESCL binds directly to the E(Z) histone methyltransferase via its WD region. In contrast to ESC, which is present at highest levels during embryogenesis and low levels thereafter, ESCL is continuously present throughout development and in adults. ESC/E(Z) complexes are present at high levels mainly during embryogenesis but ESCL/E(Z) complexes are found throughout development. While depletion of either ESCL or ESC by RNAi in S2 and Kc cells has little effect on E(Z)-mediated methylation of histone H3 lysine 27 (H3K27), simultaneous depletion of ESCL and ESC results in loss of di- and trimethyl-H3K27, indicating that either ESC or ESCL is necessary and sufficient for di- and trimethylation of H3K27 in vivo. While E(Z) complexes in S2 cells contain predominantly ESC, in ESC-depleted S2 cells, ESCL levels rise dramatically and ESCL replaces ESC in E(Z) complexes. A mutation in escl that produces very little protein is viable and exhibits no phenotypes but strongly enhances esc mutant phenotypes, suggesting they have similar functions. esc escl double homozygotes die at the end of the larval period, indicating that the well-known “maternal rescue” of esc homozygotes requires ESCL. Furthermore, maternal and zygotic over-expression of escl fully rescues the lethality of esc null mutant embryos that contain no ESC protein, indicating that ESCL can substitute fully for ESC in vivo. These data thus indicate that ESC and ESCL play similar if not identical functions in E(Z) complexes in vivo. Despite this, when esc is expressed normally, escl appears to be entirely dispensable, at least for development into morphologically normal fertile adults. Furthermore, the larval lethality of esc escl double mutants, together with the lack of phenotypes in the escl mutant, further suggests that in wild-type (esc⁺) animals it is the post-embryonic expression of esc, not escl, that is important for development of normal adults. Thus escl appears to function in a backup capacity during development that becomes important only when normal esc expression is compromised.     

c-kit marks late retinal progenitor cells and regulates their differentiation in developing mouse retina

Retinal progenitor cells are believed to display altered proliferation and differentiation during retinal development, suggesting that retinal progenitor cell populations are not homogeneous. However, the composition of progenitor cell populations is not known, due in part to the lack of known surface markers identifying distinct stages of retinal progenitor cells. We found a dramatic change in the expression profile of the cell surface antigens c-kit and stage-specific embryonic antigen-1 (SSEA-1) in retinal progenitor cells during development. While SSEA-1 was expressed early in development, c-kit expression peaked in late stage progenitor cells. The identification of these developmental markers enabled us to characterize distinct sub-populations of retinal progenitor cells. Progenitor cell subpopulations expressing either SSEA-1, c-kit, or both showed different proliferation and differentiation abilities. Although SSEA-1-positive cells were augmented by beta-catenin signaling, c-kit-positive cells were positively regulated by Notch signaling. Taken together, our data suggest that c-kit and SSEA-1 can be used to spatiotemporally differentiate retinal progenitor populations that have intrinsically distinct characteristics. Prolonged expression of c-kit by a retrovirus resulted in the promotion of proliferation and the appearance of nestin-positive cells in the presence of the c-kit ligand, stem cell factor (SCF). This suggests a role for c-kit, Notch, and the beta-catenin signaling network in retinal development.     

Extracellular matrix is required for the survival and differentiation of transplanted hepatic progenitor cells

Engelbreth-Holm-Swarm (EHS) gel has been reported to maintain the mature hepatocyte phenotypes in primary cultured hepatocytes. We investigated the effect of EHS gel on the differentiation of fetal liver cells, which contain stem/progenitor cells. The isolated fetal liver cells cultured on EHS gel formed a spherical shape and increased liver-specific gene expressions compared with cells cultured on collagen. The hepatic progenitor cells that were transplanted subcutaneously to BALB/c nude mice could survive and express hepatocyte marker alpha-fetoprotein when the cells were suspended with EHS gel. These findings demonstrate that EHS gel supports cytodifferentiation from immature progenitor cells to hepatocytes and maintain its differentiated phenotypes in vitro and in vivo.     

The p75 receptor is required for BDNF-induced differentiation of neural precursor cells

Epidermal growth factor (EGF)-treated neurospheres from fetal forebrain contain multipotential cells capable of neuronal, astrocytic, and oligodendroglial differentiation. These neural precursor cells express the TrkB as well as the neurotrophin receptor p75 (p75NTR), suggesting that they are BDNF responsive. In this study, we test whether the p75NTR plays a role in the differentiation of these neural precursor cells in vitro. Activation of the TrkB and the p75NTR by the addition of BDNF facilitates neuronal commitment and marked neurite genesis. However, no promotion of neuronal commitment by BDNF was observed in the neural precursor cells from mice carrying a mutation in the p75NTR gene. In addition, we observed a significant increase in the number of nestin-positive cells and the proliferation of the cells lacking functional p75NTR. These findings suggest that the p75NTR is required for proper neuronal fate decision as well as the differentiation of the neural precursor cells.     

Mel-18, a mammalian Polycomb gene, regulates angiogenic gene expression of endothelial cells

Mel-18 is a mammalian homolog of Polycomb group (PcG) genes. Microarray analysis revealed that Mel-18 expression was induced during endothelial progenitor cell (EPC) differentiation and correlates with the expression of EC-specific protein markers. Overexpression of Mel-18 promoted EPC differentiation and angiogenic activity of ECs. Accordingly, silencing Mel-18 inhibited EC migration and tube formation in vitro. Gene expression profiling showed that Mel-18 regulates angiogenic genes including kinase insert domain receptor (KDR), claudin 5, and angiopoietin-like 2. Our findings demonstrate, for the first time, that Mel-18 plays a significant role in the angiogenic function of ECs by regulating endothelial gene expression.     

mTOR信号通路在iPS定向分化RPE细胞中的调控机制研究

目的：探讨mTOR信号通路在iPS定向分化RPE细胞中的调控机制。方法培养iPS细胞,悬浮培养后形成拟胚体EB,诱导分化为RPE细胞。通过免疫细胞化学的方法,观察iPS-RPE细胞分化一个月后特异性蛋白（RPE65、LRAT、zo-1）的表达。同时通过Q-PCR,Western Blotting的方法检测iPS-RPE在不同分化时间点（分化1个月、2个月、3个月）上,iPS-RPE细胞中特异性基因、蛋白的表达变化以及mTOR信号通路的活性。最后应用雷帕霉素抑制iPS-RPE细胞中mTOR的通路,进一步观察iPS-RPE细胞中的蛋白表达变化。Q-PCR采用单因素方差分析（One-Way ANOVA）进行组间比较。结果荧光显微镜观察到iPS-RPE细胞在分化1个月时,表达RPE65、LRAT、zo-1蛋白。与对照组iPS比较,Q-PCR结果显示,实验组RPE65在分化1个月,2个月,3个月时的表达量分别为0.84±0.13,4.8±1.1,20.3±4.9（P=0.000）;Best1分化1个月,2个月,3个月时的表达量分别为1.5±0.16,2.3±0.68,11.78±1.57（P=0.000）;MerTK在分化1个月,2个月,3个月时的表达量分别为4.12±1.94,1.87±0.76,15.53±1.33（P=0.000）,CK18分化1个月,2个月,3个月时的表达量分别为2.4±0.63,2.3±0.37,9.67±1.44（P=0.000）,Western Blotting结果也表明,随着分化时间延长,iPS-RPE细胞中特异性蛋白（BEST1、catenin、MerTK）表达量有显著提高,而mTOR信号通路的活性受到抑制。与对照组（加DMSO）比较,雷帕霉素处理获得的iPS-RPE细胞中BEST1、MerTK、ck18蛋白表达量上升不是很明显,catenin蛋白显著提高。结论建立了体外高等分化、功能高效的iPS-RPE细胞,随iPS-RPE细胞分化时间延长,mTOR信号通路的活性是逐步抑制的。     

SSEA-1 marks regionally restricted immature subpopulations of embryonic retinal progenitor cells that are regulated by the Wnt signaling pathway

Identification and expansion of retinal progenitor cells are critical issues from both scientific and clinical aspects. Here, we identified SSEA-1 (CD15) as a novel surface antigen that can be used to define immature retinal progenitor cells. SSEA-1-expressing retinal cells were found in the peripheral region of the early embryonic mouse retina, and then their number dramatically disappeared along with retinal development. FACS analysis showed that the cells strongly positive for SSEA-1 co-expressed Ki67 proliferation antigen in all the developmental stages examined. The SSEA-1-expressing cells formed larger colonies than the non-expressing ones in retinal re-aggregation cultures. Moreover, late onset of rhodopsin expression was observed in SSEA-1-positive progenitor cells, supporting the idea that these cells have an intrinsically immature character. Differential expression of Wnt signal-related genes between SSEA-1-positive and -negative subpopulations of retina cells was revealed, and the expression of constitutively active forms of Wnt signaling molecules resulted in a greater number of SSEA-1-positive cells. In light of all of the data taken together, we propose SSEA-1 to be a surface marker to define a regionally restricted immature subset of progenitor cells of mouse neural retina, with SSEA-1 expression by them positively regulated by Wnt signals.