Macrae, T. A. | Search bioRxiv

bioRxiv2020

The deubiquitinase Usp9x regulates PRC2-mediated chromatin reprogramming during mouse development

ABSTRACTPluripotent cells of the mammalian embryo undergo extensive chromatin rewiring to prepare for lineage commitment after implantation. Repressive H3K27me3, deposited by Polycomb Repressive Complex 2 (PRC2), is reallocated from large gene-distal blankets in pre-implantation embryos to mark promoters of developmental genes. The factors that mediate this global redistribution of H3K27me3 are unknown. Here we report a post-translational mechanism that destabilizes PRC2 to constrict H3K27me3 during lineage commitment. Using an auxin-inducible degron system, we show that the deubiquitinase Usp9x is required for mouse embryonic stem (ES) cell self-renewal. Usp9x-high ES cells have high PRC2 levels and bear a chromatin and transcriptional signature of the pre-implantation embryo, whereas Usp9x-low ES cells resemble the post-implantation, gastrulating epiblast. We show that Usp9x interacts with, deubiquitinates and stabilizes PRC2. Deletion of Usp9x in post-implantation embryos results in the derepression of genes that normally gain H3K27me3 after gastrulation, followed by the appearance of morphological abnormalities at E9.5, pointing to a recurrent link between Usp9x and PRC2 during development. Usp9x is a marker of “stemness” and is mutated in various neurological disorders and cancers. Our results unveil a Usp9x-PRC2 regulatory axis that is critical at peri-implantation and may be redeployed in other stem cell fate transitions and disease states.Competing Interest StatementThe authors have declared no competing interest.View Full Text

molecular biology↗

bioRxiv2017

The transcriptionally permissive chromatin state of ES cells is acutely tuned totranslational output

A permissive chromatin environment coupled to hypertranscription is critical to drive the rapid proliferation of Embryonic Stem (ES) cells and peri-implantation embryos. We carried out a genome-wide screen to systematically dissect the regulation of the euchromatic state of ES cells. The results reveal that activity of cellular growth pathways, prominently protein synthesis, perpetuates the euchromatic state and hypertranscription of ES cells. Acute, mild inhibition of translation results in rapid depletion of euchromatic marks in ES cells and blastocysts, concurrent with delocalization of RNA polymerase II and reduction in nascent transcription. Remarkably, reduced translational output leads to rewiring of open chromatin within 3 hours, including decreased accessibility at a subset of active developmental enhancers and increased accessibility at histone genes and transposable elements. Using a proteome-scale analysis, we show that several euchromatin regulators are unstable proteins and thus continuously depend on a high translational output. We propose that this mechanistic interdependence of euchromatin, transcription and translation sets the pace of proliferation at peri-implantation and may be employed generally by stem/progenitor cells.

molecular biology↗