Oct4 is required for lineage priming in the developing inner cell mass of the mouse blastocyst

Abstract

The transcription factor Oct4 is required in vitro for establishment and maintenance of embryonic stem cells and for reprogramming somatic cells to pluripotency. In vivo, it prevents the ectopic differentiation of early embryos into trophoblast. Here, we further explore the role of Oct4 in blastocyst formation and specification of epiblast versus primitive endoderm lineages using conditional genetic deletion. Experiments involving mouse embryos deficient for both maternal and zygotic Oct4 suggest that it is dispensable for zygote formation, early cleavage and activation of Nanog expression. Nanog protein is significantly elevated in the presumptive inner cell mass of Oct4 null embryos, suggesting an unexpected role for Oct4 in attenuating the level of Nanog, which might be significant for priming differentiation during epiblast maturation. Induced deletion of Oct4 during the morula to blastocyst transition disrupts the ability of inner cell mass cells to adopt lineage-specific identity and acquire the molecular profile characteristic of either epiblast or primitive endoderm. Sox17, a marker of primitive endoderm, is not detected following prolonged culture of such embryos, but can be rescued by provision of exogenous FGF4. Interestingly, functional primitive endoderm can be rescued in Oct4-deficient embryos in embryonic stem cell complementation assays, but only if the host embryos are at the pre-blastocyst stage. We conclude that cell fate decisions within the inner cell mass are dependent upon Oct4 and that Oct4 is not cell-autonomously required for the differentiation of primitive endoderm derivatives, as long as an appropriate developmental environment is established.

The molecular underpinnings of totipotency

“…Thus mouse mutants of many of the genes that are coexpressed at early stages, such as Oct4, Nanog and Gata6, can develop past these early time points and can undergo some aspects of lineage specification [49][50][51][52][53]. Hence, individually, these factors may not be explicitly required for sustaining a totipotent state.…”

Lessons learned from functional assessment of pluripotency-associated transcription factors during early embryogenesis and embryonic stem cells

“…The silencing of OCT4 causes the formation of blastocysts lacking a pluripotent ICM (Table 1), thus with developmental potential restricted to trophoblastderived lineages (Nichols et al, 1998). Curiously, trophoblast cells require paracrine signaling from pluripotent cells, to retain their bona fide state and viability (Nichols et al, 1998;Le Bin et al, 2014). Although cleavage-stage embryonic development occurs without OCT4, the segregation between epiblast and primitive endoderm is extinguished in ICM cells lacking OCT4 (Le Bin et al, 2014).…”

“…Curiously, trophoblast cells require paracrine signaling from pluripotent cells, to retain their bona fide state and viability (Nichols et al, 1998;Le Bin et al, 2014). Although cleavage-stage embryonic development occurs without OCT4, the segregation between epiblast and primitive endoderm is extinguished in ICM cells lacking OCT4 (Le Bin et al, 2014).…”

From blastocyst to gastrula: gene regulatory networks of embryonic stem cells and early mouse embryogenesis

“…However, unlike Sox2, Oct4 expression does not become restricted to the Epi after implantation [20,111]. Recent studies have demonstrated that Oct4 is required for the maintenance of PrE-specific gene expression, which is disrupted in the absence of zygotic OCT4 protein [59,60]. Notably, this requirement for Oct4 cannot be rescued by exogenous FGF, demonstrating that Oct4 acts downstream of FGF signalling and plays a cell-autonomous as well as non-cell-autonomous role in PrE specification [59,60].…”