Ovary-specific depletion of the nuclear receptor Nr5a2 compromises expansion of the cumulus oophorus but not fertilization by intracytoplasmic sperm injection

The orphan nuclear receptor, liver receptor homolog-1 (aka Nuclear receptor subfamily 5, Group A, Member 2 (Nr5a2)), is widely expressed in mammalian tissues, and its ovarian expression is restricted to granulosa cells of activated follicles. We employed the floxed Nr5a2 (Nr5a2(f/f)) mutant mouse line and two granulosa-specific Cre lines, Anti-Mullerian hormone receptor- 2 (Amhr2Cre) and transgenic cytochrome P450 family 19 subfamily A polypeptide 1 (tgCyp19Cre), to develop two tissue- and time-specific Nr5a2 depletionmodels: Nr5a2(Amhr2-/-) and Nr5a2(Cyp19-/-). In the Nr5a2(Cyp19-/-) ovaries, Nr5a2 was depleted in mural granulosa, but not cumulus cells. We induced follicular development in mutant and wild-type (control, CON) mice with equine chorionic gonadotropin followed 44 h later treatment with human chorionic gonadotropin (hCG) to induce ovulation. Both Nr5a2(Amhr2-/-) and Nr5a2(Cyp19-/-) cumulus-oocyte complexes underwent a reduced degree of expansion in vitro relative to wild-type mice. We found downregulation of epiregulin (Ereg), amphiregulin (Areg), betacellulin (Btc) and tumor necrosis factor stimulated gene-6 (Tnfaip6) transcripts in Nr5a2(Amhr2-/-) and Nr5a2(Cyp19-/-) ovaries. Tnfaip6 protein abundance, by quantitative immunofluorescence, was likewise substantially reduced in the Nr5a2-depleted model. Transcript abundance for connexin 43 (Gja1) in granulosa cells was lower at 0 h and maximum at 8 h post-hCG in both Nr5a2(Amhr2-/-) and Nr5a2(Cyp19-/-) follicles, while Gja1 protein was not different prior to the ovulatory signal, but elevated at 8 h in Nr5a2(Amhr2-/-) and Nr5a2(Cyp19-/-) follicles. In both mutant genotypes, oocytes can mature in vivo and resulting embryos were capable of proceeding to blastocyst stagein vitro. We conclude that Nr5a2 is essential for cumulus expansion in granulosa cells throughout follicular development. The disruption of Nr5a2 in follicular somatic cells does not affect the capacity of the oocyte to be fertilized by intracytoplasmic sperm injection. Summary Sentence Liver receptor homolog-1 is necessary for cumulus expansion, but not fertilization of mouse oocytes.