Sox2/Oct4: A delicately balanced partnership in pluripotent stem cells and embryogenesis.

Considerable progress has been made in understanding the roles of Sox2 and Oct4 in embryonic stem cells and mammalian embryogenesis. Specifically, significant progress has been made in answering three questions about the functions of Sox2 and Oct4, which are the focus of this review. 1) Are the first or second cell lineage decisions during embryogenesis controlled by Oct4 and/or Sox2? 2) Do the levels of Oct4 and Sox2 need to be maintained within narrow limits to promote normal development and to sustain the self-renewal of pluripotent stem cells? 3) Do Oct4 and Sox2 work closely together or is the primary role of Sox2 in pluripotent cells to ensure the expression of Oct4? Although significant progress has been made in answering these questions, additional studies are needed to resolve several important remaining issues. Nonetheless, the preponderance of the evidence suggests there is considerable crosstalk between Sox2 and Oct4, and further suggests Sox2 and Oct4 function as molecular rheostats and utilize negative feedback loops to carefully balance their expression and other critical genes during embryogenesis. This article is part of a Special Issue entitled: The Oct transcription factor family, edited by Dr. Dean Tantin.

Rizzino A ，Wuebben EL 《-》

Transient pairing of homologous Oct4 alleles accompanies the onset of embryonic stem cell differentiation.

The relationship between chromatin organization and transcriptional regulation is an area of intense investigation. We characterized the spatial relationships between alleles of the Oct4, Sox2, and Nanog genes in single cells during the earliest stages of mouse embryonic stem cell (ESC) differentiation and during embryonic development. We describe homologous pairing of the Oct4 alleles during ESC differentiation and embryogenesis, and we present evidence that pairing is correlated with the kinetics of ESC differentiation. Importantly, we identify critical DNA elements within the Oct4 promoter/enhancer region that mediate pairing of Oct4 alleles. Finally, we show that mutation of OCT4/SOX2 binding sites within this region abolishes inter-chromosomal interactions and affects accumulation of the repressive H3K9me2 modification at the Oct4 enhancer. Our findings demonstrate that chromatin organization and transcriptional programs are intimately connected in ESCs and that the dynamic positioning of the Oct4 alleles is associated with the transition from pluripotency to lineage specification.

Hogan MS ，Parfitt DE ，Zepeda-Mendoza CJ ，Shen MM ，Spector DL ... -  《-》

Pluripotent genes in avian stem cells.

Embryonic stem (ES) cells were first isolated in 1981 in the mouse from the in vitro proliferation of the inner cell mass of a 3.5 days post-coitum (dpc) blastocyst. Later on, epiblast stem cells (EpiSC) were identified from in vitro culture of the epiblast of a 6.5 dpc mouse embryo, leading to the concept of naïve and primed stem cells. Among non-mammalian species, ES cells have been characterized both in birds and fish; here, we focus on cells derived from chicken and the pluripotent associated markers such as OCT4, SOX2, NANOG, and KLF, previously identified in mammalian cells. In this review, we present both published and original data regarding the involvement of those pluripotent associated genes in the ES cells and early embryo of chicken.

Jean C ，Aubel P ，Soleihavoup C ，Bouhallier F ，Voisin S ，Lavial F ，Pain B ... -  《-》

Simultaneous overexpression of Oct4 and Nanog abrogates terminal myogenesis.

Lang KC ，Lin IH ，Teng HF ，Huang YC ，Li CL ，Tang KT ，Chen SL ... -  《-》

Analysis of co-expression of OCT4, NANOG and SOX2 in pluripotent cells of the porcine embryo, in vivo and in vitro.

To derive porcine embryonic stem (ES) cell lines, the time window during which porcine embryos contain pluripotent cells that are predisposed to undifferentiated self-renewal in vitro must be identified. Therefore we first studied the spatial and temporal expression pattern of key factors in pluripotency and lineage segregation of blastocyst-stage porcine embryos between embryonic days (E) 6.5 and E10.5 using whole mount in situ hybridization, quantitative reverse transcription (RT)-PCR and whole mount immunofluorescence. Expression of NANOG and SOX2 was detected in both the ICM and epiblast, while OCT4 expression became restricted to the epiblast at E9.5. Surprisingly ICM and epiblast cells also expressed CK18. Consequently, growth factors which sustain the undifferentiated growth of human ES cells and mouse epiblast stem cells (EpiSCs) were tested for their ability to sustain undifferentiated self-renewal of porcine ICM and epiblast cells in vitro. Cultures of ICM cells resulted in a higher percentage of primary colonies with an ES-like morphology compared to primary cultures derived from epiblast cells. These undifferentiated colonies sustained expression of OCT4, NANOG, SOX2 and CK18. The expression of CK18 suggests that these cells are more similar to human ES cells and mouse EpiSCs than to mouse ES cells. Although undifferentiated cultures were maintained for limited passages, ICM and epiblast cultures rapidly differentiated into cell types of mesodermal, ectodermal, and endodermal origin, as characterized by RT-PCR. These results demonstrate that porcine ICM and epiblast cells can not be cultured in vitro with currently used human ES cell culture conditions. Importantly however, the trio of OCT4, NANOG and SOX2, which are known to form an autoregulatory network for pluripotency in other systems, are co-expressed also by porcine epiblasts, and by undifferentiated primary colonies in culture.

du Puy L ，Lopes SM ，Haagsman HP ，Roelen BA ... -  《-》