The E2 SUMO-conjugating enzyme UBE2I coordinates the oocyte and zygotic transcriptional programs

In mammals, meiotically competent oocytes develop cyclically during ovarian folliculogenesis. During folliculogenesis, prophase I arrested oocytes are transcriptionally active, producing and storing transcripts required for their growth and for early stages of embryogenesis prior to the maternal to zygotic transition. Defective oocyte development during folliculogenesis leads to meiotic defects, aneuploidy, follicular atresia, or non-viable embryos. Here we generated a novel oocyte-specific knockout of the SUMO E2 ligase, Ube2i, using Zp3-cre to test its function during folliculogenesis. Ube2i Zp3-cre+ female mice are sterile with oocytes that arrest in meiosis I with defective spindles and chromosome alignment. Fully grown mutant oocytes abnormally maintain transcription but downregulate maternal effect genes and prematurely activate the zygotic transcriptional program. Thus, this work uncovers UBE2i as a novel orchestrator of chromatin and transcriptional regulation in mouse oocytes. Teaser Oocyte-specific deletion of Ube2i causes loss of transcriptional repression and premature activation of the zygotic genome.