CHEMICAL-STRUCTURE OF STEROLS THAT ACTIVATE OOCYTE MEIOSIS

GONADOTROPHINS and various growth factors, but not sex steroids, can i nduce resumption of meiosis in vitro, but only in oocytes enclosed by cumulus-granulosa cells(1). Follicular purines prevent resumption of m eiosis(2,3). This process can be overcome, in vitro, by a transient el evation of cyclic AMP resulting in the production of a diffusible meio sis-inducing substance secreted by the cumulus cells(4). A meiosis-ind ucing activity has been detected in gonads of different species, for e xample, in preovulatory follicular fluid of women(5) and in mouse test es(6). We report here the isolation and characterization of meiosis-ac tivating sterols from human follicular fluid and bull testes and the s ynthesis of two closely related C-29 sterols. All these sterols induce a resumption of meiosis in cultured cumulus-enclosed and naked mouse oocytes indicating their nonspecificity across species and sex. This f amily of sterols is for the first time considered crucial to meiosis.