Transcriptomic Profiling of the Oocyte-Cumulus-granulosa Cell Complex from Estrogen Receptor Beta Knockout Mice

OBJECTIVE:To study the role of estrogen receptor β in follicle development and maturation and the response to gonadotropin stimulation aiming at superovulation. DESIGN:Experimental study and transcriptomic analysis. SETTING:Karolinka Institutet, medical university. ANIMAL(S):Healthy wild-type (WT) and estrogen receptor β knockout (Esr2-KO) female mice undergoing superovulation at 4 weeks, 7 weeks, and 6 months of age. INTERVENTION(S):Not applicable. MAIN OUTCOME MEASURE(S):Oocyte yield after superovulation, transcriptomic profiling of cumulus-granulosa cell complexes and oocytes, and immunohistochemical analyses. RESULT(S):Superovulation of estrogen receptor β (ERβ) knockout mice resulted in reduced oocyte yield at 6 months of age compared with WT mice, but younger mice had similar yields. RNA-seq analysis of cumulus cells from superovulated WT and Esr2-KO mice identified genes and pathways associated with among others adhesion, proliferation, Wnt-signaling, and placed ERβ in bipotential granulosa cell cluster. Loss of ERβ increased expression of the other estrogen receptors Esr1 and Gper1. CONCLUSION(S):Our results show that ERβ has an important role in regulating ovulation in response to exogenous gonadotropins in 6-month-old mice, but not in younger mice. Our transcriptomic and immunohistochemical observations suggest a dysregulation of the granulosa cell communication and lack of tight coordination between granulosa cell replication and antrum expansion. A significant upregulation of other estrogen receptors may support a compensatory mechanism sustaining fertility during younger age in Esr2-KO mice.