Gatekeeper of pluripotency: a common Oct4 transcriptional network operates in mouse eggs and embryonic stem cells

Abstract

Background: Oct4 is a key factor of an expanded transcriptional network (Oct4-TN) that governs pluripotency and self-renewal in embryonic stem cells (ESCs) and in the inner cell mass from which ESCs are derived. A pending question is whether the establishment of the Oct4-TN initiates during oogenesis or after fertilisation. To this regard, recent evidence has shown that Oct4 controls a poorly known Oct4-TN central to the acquisition of the mouse egg developmental competence. The aim of this study was to investigate the identity and extension of this maternal Oct4-TN, as much as whether its presence is circumscribed to the egg or maintained beyond fertilisation.

Results: By comparing the genome-wide transcriptional profile of developmentally competent eggs that express the OCT4 protein to that of developmentally incompetent eggs in which OCT4 is down-regulated, we unveiled a maternal Oct4-TN of 182 genes. Eighty of these transcripts escape post-fertilisation degradation and represent the maternal Oct4-TN inheritance that is passed on to the 2-cell embryo. Most of these 80 genes are expressed in cancer cells and 37 are notable companions of the Oct4 transcriptome in ESCs.

Conclusions: These results provide, for the first time, a developmental link between eggs, early preimplantation embryos and ESCs, indicating that the molecular signature that characterises the ESCs identity is rooted in oogenesis. Also, they contribute a useful resource to further study the mechanisms of Oct4 function and regulation during the maternal-to-embryo transition and to explore the link between the regulation of pluripotency and the acquisition of de-differentiation in cancer cells.

Figure 1

Microarray-based analysis of the transcription profile of developmentally incompetent and competent MII oocytes and 2-cell embryos. (A) Major biological processes and functions found when comparing the transcription profile of MII^NSN vs. MII^ctrl oocytes and number of up- and down-regulated genes in each of these processes. (B) Major biological processes and functions found when comparing the transcription profile of 2-cell^NSN vs. 2-cell^ctrl embryos and number of up- and down-regulated genes in each of these processes.

Figure 2

List of OCT-4-regulated genes expressed in both MII oocytes and 2-cell embryos. Comparison of gene expression is made between MII^NSN vs. MII^ctrl or 2-cell^NSN vs. 2-cell^ctrl. Red box, up-regulated; green box, down-regulated; blank box, not differentially expressed. The hypergeometric test proved that the up- (MII^NSN oocytes) and down-regulated (2-cell^NSN embryos) pattern of expression of the majority genes (*) was not a stochastic event (p = 0.0039).

Figure 3

Immuno detection of the RPS20 and DNMT3L proteins in MII oocytes and 2-cell embryos. (A) MII^ctrl and MII^NSN oocytes and in (B) 2-cell^ctrl and 2-cell^NSN embryos. (a, c, e, g and a', c', e', g'), antibodies staining; (b, d, f, h and b', d', f', h'), merge between antibodies staining and DAPI counterstaining. Scale bar, 20 μm.

Figure 4

Venn diagram illustrating distinct and overlapping gene expression patterns in MII oocytes and 2-cell embryos. Boxes, list of genes belonging to each specific group; genes in bold, OCT4-regulated genes.

Figure 5

Oct4 transcriptional network. Genes expressed in both MII oocytes and 2-cell embryos. Green box, down-regulated; red box, up-regulated; blue font, OCT4-regulated gene; highlighted in grey, OCT4-correlated gene (Campbell et al., 2007).

Figure 6

Gene clusters singled out in the expanded Oct4-TN. Green lines, MeSH annotations; orange lines, MeSH and GO annotations; grey lines, GO annotations. Increasing line width indicates stronger annotation relationship.

Figure 7

The Oct4-TN genes expressed in MII oocytes and in 2-cell embryos. Black frame, 80 Oct4-OETN genes expressed in both MII oocytes and 2-cell embryos; highlighted in yellow, Oct4.

Figure 8

OCT4-regulated genes expressed in eggs, 2-cell embryos and ESCs. This core Oct4-TN may provide a link between eggs, early preimplantation embryos and ESCs.