TRIM28-dependent SUMOylation protects the adult ovary from the male pathway (ChIP-Seq 2)

We study the role of the protein Trim28 in the maintenance of sexual identity of the adult ovary. With the help of conditional knock out (cKO) of Trim28 using the Nr5a1:Cre, we observed that deletion of the Trim28 gene in granulosa cells of the adult ovary induces their transdifferentiation into Sertoli cells, the supporting cell lineage of the testicular seminiferous tubules. FOXL2 expression has disappeared and follicles were completely remodeled into tubular structures with cells that expressed the Sertoli cell markers SOX8, SOX9 and DMRT1. Histological analysis confirmed the progressive reorganization of ovarian follicles into tubular structures and the and the transdifferentiation of granulosa cells by cells with a Sertoli cell morphology. TRIM28 acts as a SUMO-E3 ligase by interacting with the SUMO-E2 conjugating enzyme UBC9 (encoded by the Ube2i gene) via the Plant homeodomain (PHD), and can self-SUMOylate. To study in vivo the role of TRIM28-dependent SUMOylation, we generated a point mutation in exon 13 of mouse Trim28 within the PHD domain of the TRIM28 protein (C651F) that abrogates its SUMO-E3 ligase activity. We generated Trim28Phd/cKO mice (termed PHD mutant). Like in cKO ovaries, FOXL2 expression was undetectable, whereas we observed expression of the Sertoli cell markers SOX9, SOX8 and DMRT1 within structures organized in pseudo-tubules in PHD ovaries. Our results indicate that maintenance of the female pathway in the adult ovary depends on the E3-SUMO ligase activity of TRIM28. To determine whether in PHD mice, SUMOylation was modified genome-wide, we performed quantitative SUMO1 and SUMO2 ChIP-seq analyses with adult 8-weeks-old ovaries from control, cKO and PHD.