The molecular landscape of developmental pausing in mammals

Abstract

Many mammals can control the timing of birth by temporarily suspending development which is marked by a reduction of metabolic activity. This interruption in the development process is called diapause is specific to blastocyst-stage embryos and is an apparent response to tide over adverse environmental and nutritional conditions. The establishment of diapause is an active process involving extensive rewiring of the epigenetic, transcriptomic and metabolic landscape of the embryo. How the above three cellular processes are coordinately re-wired during dormancy entry is not known. Here I show that the regulatory function of miRNAs is indispensable for the mouse embryos entering into the diapause state. Without the miRNA function mouse ESCs and embryos suffer developmental collapse upon mTORi-mediated diapause induction. Small RNA sequencing of single mouse embryos showed specific miRNAs to be upregulated during diapause induction. In silico miRNA-protein network of diapause was developed by the integration of small RNA sequencing data together with computationally predicted miRNA targets. The network showed miRNA-mediated regulation of nuclear and cytoplasmic bodies along with RNA splicing which are perturbed in miRNA null mouse ESCs. The study also shows nutrient and autophagy regulator TFE3 to be the upstream regulator for the expression of dormancy-associated miRNAs, linking cytoplasmic mTOR activity to nuclear miRNA biogenesis.

It is unknown whether the capacity to pause is a conserved trait across mammals, more specifically in humans. Mouse and humans show similar patterns of mTOR expression during pre-implantation development, suggesting the involvement of the primordial pathway in blastocyst development and timing in both species. Here I show human blastoids and pluripotent cells in naïve and naïve-like states retain the capacity to pause via mTOR inhibition and the pausing is functionally reversible even at the molecular level.

Taken together the above findings suggest that the development of human embryos may be controllable and that miRNAs play a critical regulatory role in bringing transcriptional re-wiring in mouse embryos for successful entry into dormancy.