HYALURONAN SYNTHESIS BY MOUSE CUMULUS CELLS IS REGULATED BY INTERACTIONS BETWEEN FOLLICLE-STIMULATING-HORMONE (OR EPIDERMAL GROWTH-FACTOR) AND A SOLUBLE OOCYTE FACTOR (OR TRANSFORMING GROWTH-FACTOR BETA(1))

Expansion of the cumulus cell oocyte complex (COC) in the preovulatory mammalian follicle requires a transient induction of hyaluronan (HA) synthesis by the cumulus cells. We studied the interactions of known f actors that regulate this process by isolating compact COCs from mice and inducing their expansion in vitro. Maximum HA synthesis requires e ither follicle-stimulating hormone (FSH) or epidermal growth factor (E GF) in combination with either a soluble factor(s) produced by the ooc yte or transforming growth factor beta(1). FSH (or EGF) exerts its eff ects during the first 2 h of incubation, before HA synthesis actually beans, The oocyte factor(s) (or transforming growth factor beta(1)) ex erts its effects from 2 h onwards and must be continuously present thr oughout the subsequent similar to 10 h to achieve a maximum level of H A synthesis, FSH stimulates intra cellular cAMP synthesis, which corre lates with net HA production up to similar to 14 fmol/COC at 5 ng/ml F SH; however, higher concentrations of FSH increase cAMP levels similar to 10-fold higher with no additional effect on HA synthesis, EGF at s aturating concentrations for HA synthesis does not stimulate cAMP abov e basal levels, Tyrosine kinase inhibitors genistein and tyrphostin AG 18 nearly abolish the HA synthesis response to EGF and inhibit the res ponse to FSH by similar to 60%, suggesting that a tyrosine kinase acti vity is involved for both factors, whereas FSH also operates partially through another signaling pathway, Actinomycin D abolishes HA synthes is if added at the beginning of culture and reduces HA synthesis by si milar to 50% if added between 6-12 h when HA synthesis is normally max imal, The results suggest that regulation of HA synthesis is primarily controlled at the transcriptional level.