Trim33 regulates early maturation of mouse embryoid bodies in vitro.

Embryonic stem cells (ESCs) are an established model for investigating developmental processes, disease conditions, tissue regeneration and therapeutic targets. Previous studies have shown that tripartite motif-containing 33 protein (Trim33) functions as a chromatin reader during Nodal-induced mesoderm induction. Here we report that despite reduced proliferation, mouse ESCs deficient in Trim33 remained pluripotent when cultured under non-differentiating conditions. However, when induced to differentiate to embryoid bodies (EBs), the mutant cultures showed increased cell shedding and apoptosis at day 3 of differentiation. Gene set enrichment analysis (GSEA) indicated that several molecular functions associated with cell survival, transcriptional/translational activity and growth factor signaling were affected already by the second day of differentiation in Trim33-deficient EBs. Consistent with increased apoptosis, expression of Rac1, a critical factor for EB cell survival, was reduced in Trim33 mutant EBs. In addition, a set of genes involved in regulation of pluripotency was upregulated in mutant EBs. Our results suggest that Trim33 regulates early maturation of mouse embryoid bodies in vitro.