227. FSH receptor expression in small human ovarian follicles

Abstract

Follicle-stimulating hormone (FSH) is pivotal in ovarian follicle development; the granulosa cells are the targets of FSH action in the ovary via FSH receptors. Granulosa cell growth and division mark initial follicle recruitment. The acquisition of FSH receptors on granulosa cells is regarded as a key event in hormone responsiveness and consequently follicle development. Due to the low abundance of FSH receptors and low expression of its mRNA it has been difficult to definitively characterise FSH receptor expression patterns. Here, localisation of FSH receptor in different follicle populations has been assessed with in situ hybridisation and real-time PCR of laser microdissected samples. We have used non-radioactive in situ hybridisation to investigate FSH receptor mRNA on a wide range of follicle stages. Biopsies from healthy fertile women (28–33 years) were frozen, embedded and cryosectioned at 10 µm. DIG-labelled RNA probes were designed to detect all splice variants. Hybridised probes were detected with NBT/BCIP in a colorimetric reaction. Secondly, follicles of different morphometric stages were isolated with a laser microscope. RNA extraction, reverse transcription and real-time PCR were used to confirm RNA presence and quantify relative expression. All follicle stages (from primordial to large antral) showed the presence of FSH receptor mRNA in their granulosa cells; sense controls were negative. Observations from real-time PCR indicate FSH receptor mRNA is present in all follicle stages observed and relative expression levels increase over early follicle development. These results challenge the existing doctrine that FSH receptor is absent in the smallest follicles. This suggests initial follicle recruitment may involve gonadotrophins. The use of sensitive molecular techniques will be crucial in elucidating this further.