Endocrine Abstracts

The G protein-coupled receptor (GPCR), follicle stimulating hormone receptor (FSHR) plays a critical role in ovarian function and reproduction, with multiple functions in follicle growth, maturation, survival, and steroid hormone production. Yet how FSH/FSHR mediates these pleiotrophic physiological roles remains unknown. Numerous studies indicate GPCRs can regulate and diversify their actions through receptor-receptor association and the formation of dimers/oligomers. Moreover, our recent data in heterologous cell lines expressing FSHR suggests that differences in signal amplitude may in part be mediated by modulating FSHR homomerisation. However, the physiological significance of FSHR oligomerisation in coordinating ovarian functions remains unknown. This study therefore aimed to characterise a novel N-terminally FLAG-tagged knock-in FSHR mouse model, to understand the physiological roles of FSHR oligomerisation in modulating ovarian functions. Phenotypic characterisation of FLAG-FSHR mice revealed that ovarian and uterine weights were comparable to wild type (WT), suggesting FSH-mediated oestrogenic actions were maintained in the FLAG-knock in mice. Histological analysis of ovaries showed the presence of follicles at all stages of development and corpora lutea in WT and FLAG-FSHR mice, indicating intact follicle development and ovulation. Breeding studies confirmed the fertility of FLAG-FSHR mice, showing comparable litter sizes and interbreeding intervals to WT animals. As these data suggested that the insertion of the FLAG tag did not affect FSHR-ovarian functions, analysis of FSHR homomerisation in granulosa cells was conducted. Super-resolution imaging via PD-PALM revealed ~40% of FSHR were basally associated, with ligand-dependent differences observed in the number and subtype of FSHR monomer, dimer and oligomer populations. These data support the utilisation of this novel FLAG-FSHR mouse model for monitoring endogenous native FSHR oligomerisation, providing an effective tool to elucidate the role of FSHR complexes in ovarian function.