Trout ovulatory proteins: Site of synthesis, regulation, and possible biological function

The mRNA transcripts for trout ovulatory proteins (TOPs) are dramatically u p-regulated at the time of ovulation. Previous studies indicated that TOPs were produced by the ovaries and were also present in the coelomic fluid th at bathes ovulated eggs. In the present study, Western analysis indicated t hat TOPs were not present in the coelomic fluid prior to ovulation and ther efore must be secreted into the coelomic fluid in targe quantities during a nd after ovulation. Using in situ hybridization and immunocytochemistry, TO P mRNA and proteins were localized to the granulosa cell layer of the posto vulatory follicle. A whole-follicle in vitro incubation system was used to look at the effects of various mediators on TOP mRNA and protein levels. Re sults of several different secondary messenger agonists suggest that TOPs a re regulated through a G protein-mediated pathway that does not involve cAM P but may involve the activation of protein kinase C. Other agonists that h ad significant effects on TOP RNA and/or protein included transforming grow th factor alpha (TGF-alpha), serine proteases, corticosteroids, bacterial l ipopolysaccharide, and the nitric oxide generator SNAP ([+/-]-S-nitroso-N-a cetylpenicillamine). Overall, while several compounds caused significant ef fects, none were able to reproduce the increase in TOP RNA and protein that occurs in vivo, suggesting that the natural mediator of TOPs may still be untested, or that a combination of mediators may be involved. Finally coelo mic fluid inhibited the growth of the Gram negative bacterium, P. aeruginos a, and this inhibition was lost following immunoprecipitation of TOPs. This suggests that one function of TOPs may be to protect ovulated eggs from ba cterial infection.