The development of a whole organism from a single fertilised egg is a tightly orchestrated process at the molecular level. Signalling pathways stimulate the expression of transcription factors that in turn coordinate the activation, repression or priming of genes through multi-protein complex assembly and chromatin remodelling at regulatory regions during key developmental transitions.
This project focuses on the role of the chromatin modifier Jmjd2c/Kdm4c in embryonic stem cell (ESC) pluripotency. Jmjd2c is a member of Jmjd2 H3K9-demethylase family, which is highly expressed in ESCs and during early mouse development, and was proposed to contribute to ESC identity. Here, Jmjd2c-depleted ESCs were generated and found to sustain an undifferentiated state. In contrast, these cells fail to execute multi-lineage differentiation, as evidenced by their inability to fully activate appropriate gene expression programs, but readily adopt an extra-embryonic endoderm-like phenotype under appropriate conditions. Moreover, Jmjd2c-knockout ESCs can transit to an early epiblast stage and be stably converted into epiblast stem cells (cEpiSCs) that harbour an immature state as highlighted by a lack of transcriptional gene priming for germ layer markers.
In order to unfold the mechanistic basis for the observed differentiation defect, genome-wide distribution of Jmjd2c was analysed by ChIP-sequencing. This revealed prominent binding to the TSS of active and bivalently marked genes, concordant with recent reports. Remarkably, acquisition of multi-lineage priming in ESCs was accompanied by Jmjd2c recruitment at poised enhancers of lineage-affiliated genes. Surprisingly, these regions were co-occupied by the H3K9-methyltransferase G9a/Ehmt2, which physically interacts with Jmjd2c and Mediator, within chromatin-bound complexes. Critically, the absence of Jmjd2c in cEpiSCs was sufficient to destabilize the assembly of enhancer protein complexes, suggesting a scaffolding role independent of its H3K9-demethylase activity. Collectively, this study uncovered a novel role for Jmjd2c in regulating gene expression at exit of the pluripotent state.