126. JAK/STAT SIGNALLING IN FOLLICULOGENESIS

Abstract

Primordial follicle activation marks the first stage of pre-pubertal ovarian folliculogenesis, and is therefore fundamental to female fertility. Entry into development is initiated by a group of pleiotropic cytokines and growth factors, originating in and acting upon both the oocyte and granulosa support cells of the ovarian follicle through the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signalling pathway. Pivotal to this process is the transcriptional regulation of target genes via STAT complexes and negative regulation by the Suppressors of Cytokine Signalling (SOCS) family of proteins. Preliminary evidence indicates that STAT3 facilitates the activation of primordial follicles, while SOCS4 counterbalances the activity of STAT3, mediating the controlled release of primordial follicles into the growing pool throughout reproductive life. Leukemia Inhibitory Factor (LIF) has been previously demonstrated as a key granulosa cell derived cytokine involved in inducing primordial follicle activation. Through both quantitative gene expression (qPCR) and immunoblotting we have demonstrated that LIF can significantly upregulate STAT3 mRNA production (~2-fold) as well as increase STAT3 protein phosphorylation within neonatal mouse ovarian explants culture. Furthermore, through the generation of a recombinant SOCS4 protein construct, and its use in subsequent protein-protein pull-downs, we were able to multiple targets involved in oocyte maturation, STAT3 interactions, and JAK/STAT signaling. These targets were also found to be significantly upregulated via qPCR analysis in neonatal mouse ovaries treated with LIF. These results support our current model for the involvement of STAT3 and SOCS4 in a basic negative feedback loop within the JAK/STAT signalling pathway that results in the regulation of primordial follicle activation and development.