转录因子Oct4、Sox2和Nanog在早期胚胎发育过程中的表达调控

胚胎发育的分子机理是现今胚胎工程及发育生物学研究迫切需要了解的。由于胚胎发育的早期阶段就是胚胎干细胞阶段,因此两者在研究上有很好的重合性。通过对调节胚胎干细胞基因转录的三个具有代表性的转录因子Oct4、Sox2和Nanog的综述,展现出胚胎发育分子机理研究概况。     

Geminin escapes degradation in G1 of mouse pluripotent cells and mediates the expression of Oct4, Sox2, and Nanog

Geminin is an essential cell-cycle protein that is only present from S phase to early mitosis in metazoan somatic cells. Genetic ablation of geminin in the mouse results in preimplantation embryonic lethality because pluripotent cells fail to form and all cells differentiate to trophoblast. Here we show that geminin is present in G1 phase of mouse pluripotent cells in contrast to somatic cells, where anaphase-promoting complex/cyclosome (APC/C)-mediated proteasomal destruction removes geminin in G1. Silencing geminin directly or by depleting the APC/C inhibitor Emi1 causes loss of stem cell identity and trophoblast differentiation of mouse embryonal carcinoma and embryonic stem cells. Depletion of cyclins A2 or B1 does not induce this effect, even though both of these APC/C substrates are also present during G1 of pluripotent cells. Crucially, geminin antagonizes the chromatin-remodeling protein Brg1 to maintain expression of Oct4, Sox2, and Nanog. Our results define a pluripotency pathway by which suppressed APC/C activity protects geminin from degradation in G1, allowing sustained expression of core pluripotency factors. Collectively, these findings link the cell cycle to the pluripotent state but also raise an unexplained paradox: How is cell-cycle progression possible in pluripotent cells when oscillations of key regulatory proteins are lost?     

Expression and role of Oct3/4, Nanog and Sox2 in regeneration of rat tracheal epithelium

Objectives:  To explore the role of Oct3/4, Nanog and Sox2 in regeneration of rat tracheal epithelium.
Materials and methods:  An ex vivo model of rat tracheal epithelial regeneration using 5-fluorouracil (5-FU) was developed, to induce injury. Expression levels of Oct3/4, Nanog and Sox2 were examined using Western blot analysis, RT-PCR or microscopically observed immunofluorescence, and cell morphological changes were observed using HE staining, during the recovery process.
Results:  Oct3/4, Nanog and Sox2 were not detectable in normal tracheal epithelium. After treatment with 5-FU, the normally proliferating tracheal epithelium desquamated and only a few cells in G0 phase of the cell cycle were left on the basement membrane and Oct3/4, Nanog and Sox2 could be observed at this time. Thereafter, the number of Oct3/4-, Nanog- and Sox2-positive cells increased gradually. When the cells differentiated into ciliate cells, mucous cells or basal cells, and restored pseudostratified mucociliary epithelium, the number of Oct3/4-, Nanog- and Sox2-positive cells decreased and gradually disappeared.
Conclusions:  G0 phase cells with resistance to 5-FU damage expressed Oct3/4, Nanog and Sox2. This indicated that these cells were undifferentiated, but had the ability to terminally differentiate into downstream-type cells. They possessed stem cell properties. The results are consistent with Oct3/4, Nanog and Sox2-expressing cells being considered as tracheal stem cells.     

米非司酮对早孕绒毛Oct4、Sox2、Nanog 表达影响*

目的:探讨米非司酮对早孕绒毛组织Oct4、Sox2、Nanog mRNA和蛋白水平表达的影响。方法:要求终止妊娠的正常早孕妇女60例,分为:负压吸宫组及服用米非司酮150mg及米索前列醇联合行药物流产组。运用Real-time PCR方法检测两组早孕绒毛组织中Oct4、Sox2、Nanog mRNA的表达;采用免疫组织化学方法检测两组早孕绒毛组织Oct4、Sox2、Nanog蛋白的定位及半定量表达情况,比较两组差异。结果:Oct4、Nanog、Sox2 mRNA在药物流产组早孕绒毛中相对表达量明显低于负压吸宫组,差异有统计学意义(相对表达量分别为:0.15±0.045;0.37±0.053;0.23±0.040,P值均<0.05);Oct4、Nanog、Sox2在药物流产组早孕绒毛蛋白表达量亦明显低于负压吸宫组,差异有统计学意义(药物流产组蛋白表达量分别为13869±541、19251±1503、139492±918明显低于负压吸宫组22017±235、30543±729、37237±710)。结论:米非司酮可以通过抑制早孕绒毛中Oct4、Sox2、Nanog表达,发挥抗早孕作用。     

SUMOylation of Tr2 orphan receptor involves Pml and fine-tunes Oct4 expression in stem cells

The Tr2 orphan nuclear receptor can be SUMOylated, resulting in the replacement of coregulators recruited to the regulatory region of its endogenous target gene, Oct4. UnSUMOylated Tr2 activates Oct4, enhancing embryonal carcinoma-cell proliferation, and is localized to the promyelocytic leukemia (Pml) nuclear bodies. When its abundance is elevated, Tr2 is SUMOylated at Lys238 and seems to be released from the nuclear bodies to act as a repressor. SUMOylation of Tr2 induces an exchange of its coregulators: corepressor Rip140 replaces coactivator Pcaf, which switches Tr2 from an activator to a repressor. This involves dynamic partitioning of Tr2 into Pml-containing and Pml-free pools. These results support a model where SUMOylation-dependent partitioning and differential coregulator recruitment contribute to the maintenance of a homeostatic supply of activating, as opposed to repressive, Tr2, thus fine-tuning Oct4 expression and regulating stem-cell proliferation.     

Heterozygous loss of Zbtb38 leads to early embryonic lethality via the suppression of Nanog and Sox2 expression

ObjectivesMammalian DNA methyltransferases are essential to re‐establish global DNA methylation patterns during implantation, which is critical for transmitting epigenetic information to the next generation. In contrast, the significance of methyl‐CpG binding proteins (MBPs) that bind methylated CpG remains almost unknown at this stage. We previously demonstrated that Zbtb38 (also known as CIBZ)—a zinc finger type of MBP—is required for mouse embryonic stem (ES) cell proliferation by positively regulating Nanog expression. However, the physiological function of Zbtb38 in vivo remains unclear.Materials and MethodsThis study used the Cre‐loxP system to generate conditional Zbtb38 knockout mice. Cell proliferation and apoptosis were studied by immunofluorescence staining. Quantitative real‐time PCR, immunoblotting and immunofluorescence were performed to investigate the molecular mechanisms.ResultsGermline loss of the Zbtb38 single allele resulted in decreased epiblast cell proliferation and increased apoptosis shortly after implantation, leading to early embryonic lethality. Heterozygous loss of Zbtb38 reduced the expression of Nanog, Sox2, and the genes responsible for epiblast proliferation, differentiation, and cell viability. Although this early lethal phenotype, Zbtb38 is dispensable for ES cell establishment and identity.ConclusionsThese findings indicate that Zbtb38 is essential for early embryonic development via the suppression of Nanog and Sox2 expression.

Heterozygous loss of Zbtb38 leads to aberrant epiblast cell proliferation and apoptosis shortly after implantation. Heterozygous loss of Zbtb38 reduced the expression of Nanog and Sox2 in ICM and epiblast.