Expression and tissue distribution of G protein-coupled oestrogen receptor 1 in the reproductive system of the laying hen

In recent years, G protein-coupled oestrogen receptor 1 (GPER1) has been revealed as an important mediator of oestrogen's action on the reproductive processes in mammals; however, its role in the avian reproductive system is not known. In the present study, it was examined whether GPER1 is present in the hen's reproductive system and if so, its mRNA and protein distribution in the ovary and oviduct. Immunolocalisation of GPER1 in the ovarian follicles and all oviductal parts (i.e.infundibulum, magnum, isthmus, shell gland and vagina) was also investigated. The GPER1 mRNA transcript and protein were detected in all of the examined tissues by real-time PCR and Western Blot analyses, respectively. The relative expression of GPER1 depended on the follicle development and the follicular wall layer (p < 0.001). It was highest in the white and yellowish follicles and lowest in the granulosa layer of F3-F1 follicles. Immunoreactivity for the GPER1 protein was most prominent in the ovarian stroma with primordial and primary follicles, white follicles and yellowish follicles. Within the oviduct, the highest level of the GPER1 transcript was in the infundibulum, while the lowest was in the magnum (p < 0.001). Moreover, protein abundance was higher (p < 0.05) in the shell gland than in the vagina. The strongest immunopositive reaction was observed in the shell gland and vagina, especially in the luminal epithelium. The obtained preliminary results indicate that the oestrogen action in the reproductive systems of female birds also involves GPER1 signalling.