Expression of osteopontin (OPN) mRNA in bovine ovarian follicles and corpora lutea

The matricellular protein osteopontin (OPN) plays a role in various physiological processes, including angiogenesis and tissue remodelling. As these processes are essential for the maintenance of ovarian physiology, the aim of the study was to investigate the expression of OPN (mRNA) in ovarian cells and to evaluate whether it can be regulated by gonadotrophins. Using conventional RT-PCR and real-time PCR, we have detected and quantified OPN mRNA as well as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA expression in bovine granulosa, theca and luteal cells. In all cells examined, both genes were found in equal amounts and no striking variations in the expression could be observed between granulosa, theca and luteal cells. Furthermore, no effect on either OPN or GAPDH mRNA expression was evident after culturing ovarian cells in the presence of gonadotrophic hormones, although the cells were still highly responsive in terms of cAMP formation. Although neither variations between different cell types nor a regulation of OPN mRNA expression by gonadotrophic hormones could be detected, the high and unambiguous mRNA expression in steroidogenic cells suggests that OPN should be added to the growing list of intraovarian factors which may be involved in ovarian physiology.