Study On The Role And Mechanism Of Oocyte-granulosa Interaction In The Induction Of Key Ovulatory Events By LH In Mice

Oogenesis in mammals is ultra-precise and sophisticated,being as the interplay among a series of signals and nutritive substances.Ovarian follicle,as the fundamental unit in the ovary,is prioritized during the study of oogenesis.Thus,the microenvironments within the follicle are vital for both granulosa cells and oocyte Scientists are universally aware of the cross-correlation between granulosa cells and oocyte which runs throughout the whole process of oogenesis.Oocyte-derived paracrine factors(ODPFs)play a vital role in this interaction.A series of biological events takes place before ovulation and after LH serge including cumulus expansion and germinal vesicle breakdown.However,whether or not the cascade reaction inducted by LH is closely related to MTOR signal pathway remains to be identifiedIn the first part of the study,we focus on identifying the mechanism underlying the interplay between granulosa cells and oocyte.By using the approaches of transcriptomic analysis herein,we explored the global changes of transcription profiles in cumulus cells after the activation of EGFR signaling both in vivo and in vitro,and investigated whether these changes are also regulated by oocytes and the oocyte-specific ODPF,GDF9 and BMP 15 heterodimer(hereafter referred to as G:B).After that,we made meticulous efforts on analyzing the level of mRNA and protein.Interestingly,among these transcripts regulated by both EGFR signaling and ODPFs,some are reported to be associated positively with the development and maturation of oocyte.Meanwhile,according to the paper published on the Journal of Cell Science by Guojing,the other study in our team explored the coincident alteration between Toiml on the MTOR signaling and the mice's cumulus cells injected with hCG.In that paper,we found that:the global changes of transcription profiles in cumulus cells after the inhibition of EGFR signaling in vitro are partly identical to the one treated with hCG in vivo in mice.To further investigate the biological roles of MTOR signal in cumulus cells,we cultured the COC with Torin1 in vitro.What has been proved is that the cumulus expansion and germinal vesicle breakdown is promoted by restraining the MTOR.Then,we detected the activation of P-Rps6,the downstream of MTORC1 signal by Immunofluorescence.It revealed a specific spatial-temporal dynamic change within 6 hours after hCG by i.p in vivo.In addition,inhibition of MTOR in vitro facilitated related expression of genes encoding of the cumulus expansion and EGF-like factors,whereas,the expression of Npr2,though extremely relevant to GVBD,was inhibited.Indeed,the P-ERK1/2 in cumulus cells was activated when cultured with Torin1.It reveals a successful ovulation but a defective acquisition of oocyte competence supporting the embryo development in the MTORF/F;Amhr2-/Cre mice.The blastocyst rate significantly decreased v.s wild type after IVF.Whether or not the follicular has developed and maturated in advance of COC remains to be investigated.Furthermore,the mechanism causing this phenotype should be excavated accordingly as well.This study indicates that the granulosa cell-oocyte regulatory loop plays an irreplaceable role in the biological events before ovulation and after LH surge,especially cumulus expansion and GVBD.There is a possibility that the ahead-of-time ovulation undermines the development capacity of oocyte and results in the declining of mice's potentia generandi.