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.

Meiotically competent oocytes in mammals undergo cyclic development during folliculogenesis. Oocytes within ovarian follicles are transcriptionally active, producing and storing transcripts required for oocyte growth, somatic cell communication, and early embryogenesis. Transcription ceases as oocytes transition from growth to maturation and does not resume until zygotic genome activation. While SUMOylation, a post-translational modification, plays multifaceted roles in transcriptional regulation, its involvement during oocyte development remains poorly understood. In this study, we generated a novel oocyte-specific knockout of the SUMO E2 enzyme, Ube2i, using Zp3-cre+, to determine how loss of oocyte SUMOylation during folliculogenesis affects their development. Ube2i Zp3-cre+ female knockout mice were sterile, with oocyte defects in meiotic competence, spindle architecture and chromosome alignment, and a premature arrest in metaphase I. Additionally, fully grown Ube2i Zp3-cre+ oocytes exhibited sustained transcriptional activity but downregulated maternal effect genes and prematurely activated genes and retrotransposons typically associated with zygotic genome activation. These findings demonstrate UBE2i is required for the acquisition of key hallmarks of oocyte development during folliculogenesis, and highlight UBE2i as a novel orchestrator of transcriptional regulation in mouse oocytes.

The regenerative potential of the endometrium is attributed to endometrial stem cells; however, the signaling pathways controlling its regenerative potential remain obscure. In this study, genetic mouse models and endometrial organoids were used to demonstrate that SMAD2/3 signaling controls endometrial regeneration and differentiation. Mice with conditional deletion of SMAD2/3 in the uterine epithelium using Lactoferrin-iCre developed endometrial hyperplasia at 12-weeks and metastatic uterine tumors by 9-months of age. Mechanistic studies in endometrial organoids determined that genetic or pharmacological inhibition of SMAD2/3 signaling disrupted organoid morphology, increased the glandular and secretory cell markers, FOXA2 and MUC1, and altered the genome-wide distribution of SMAD4. Transcriptomic profiling of the organoids revealed elevated pathways involved in stem cell regeneration and differentiation such as the bone morphogenetic protein (BMP) and retinoic acid signaling (RA) pathways. Therefore, TGFβ family signaling via SMAD2/3 controls signaling networks which are integral for endometrial cell regeneration and differentiation.