An Early Developmental Role for miRNAs in the Maintenance of Extraembryonic Stem Cells in the Mouse Embryo

Abstract

The two first cell fate decisions taken in the mammalian embryo generate three distinct cell lineages: one embryonic, the epiblast, and two extraembryonic, the trophoblast and primitive endoderm. miRNAs are essential for early development, but it is not known if they are utilized in the same way in these three lineages. We find that in the pluripotent epiblast they inhibit apoptosis by blocking the expression of the proapoptotic protein Bcl2l11 (Bim) but play little role in the initiation of gastrulation. In contrast, in the trophectoderm, miRNAs maintain the trophoblast stem cell compartment by directly inhibiting expression of Cdkn1a (p21) and Cdkn1c (p57), and in the primitive endoderm, they prevent differentiation by maintaining ERK1/2 phosphorylation through blocking the expression of Mapk inhibitors. Therefore, we show that there are fundamental differences in how stem cells maintain their developmental potential in embryonic and extraembryonic tissues through miRNAs.

Essential role of the CUL4B ubiquitin ligase in extra-embryonic tissue development during mouse embryogenesis

“…However, the inability to achieve full rescue by p21 silencing suggests that other yet-to-be identified CUL4B substrates likely also contribute to the cell cycle arrest that is triggered by CUL4B inactivation. Spruce et al [38] recently demonstrated that inhibition of p21 expression by miRNA was required to maintain the trophoblast stem cell compartment. Our findings suggest that p21 accumulation is a significant factor that contributes to the developmental defects of the extra-embryonic tissues and embryonic lethality of Cul4b-null mice.…”

MiRNA-mediated regulation of cell signaling and homeostasis in the early mouse embryo

“…1). 15 In agreement with there not being any major perturbation in Nodal signaling in embryos lacking miRNAs, mesoderm formation is initiated, although with a one day delay, in the posterior epiblast and there is no expansion of neuroectoderm markers. The delay in mesoderm formation mimics that of Nodal restriction in these embryos (Fig.…”

“…1). 15 Additionally we found that the genes coding for the Nodal processing proteins Spc1 and Spc4 are expressed in the trophoblast, the Nodal co-activator Cripto is robustly expressed in the epiblast and Lefty1 expression is not expanded in Dicer zygotic deletion of Dgcr8 in mouse has shown that miRNAs are neither required for early pre-implantation development nor trophectoderm specification. 13 Given the major role that extra-embryonic tissues have on the development of the mammalian epiblast it is necessary to consider them when analysing the effect of miRNAs deletion on embryo development.…”

“…For this reason we recently carried out an extensive analysis of the effect of Dicer deletion on both embryonic and extra-embryonic tissues of the mouse embryo. 14,15 This study has revealed different functions for miRNAs in each lineage and represents a step forward in our understanding of the regulatory networks governing early mammalian development and the role of miRNAs within them.…”

“…These were Rasa2, a GTPAse activating protein that inactivates Ras, Dusp1, a phosphatase that targets Erk and Sulf2, a sulfatase that can remove 6-O-sulfate groups When we deleted Dicer and thus depleted miRNAs in multipotent cells derived from the primitive endoderm (XEN cells), one of the first alterations we observed was a decrease in the levels of phosphorylated Erk1/2. 15 This was followed by reduced cellular proliferation, a decrease in the expression level of a number of AVE markers and an increase in the expression level of a number of extraembryonic visceral endoderm and parietal endoderm markers. Further investigation revealed that the reduced Erk signaling null mouse embryos (Fig.…”