Meiosis activating sterols (MAS) and fertility in mammals and man

In mammals two meiosis activating sterols (MAS) have been found to activate meiotic resumption in mouse oocytes, in vitro. FF-MAS (4,4-dimethyl-5 alph a-cholesta-8,14,24-triene-3 beta-ol) was extracted from human preovulatory follicular fluid and T-MAS (4,4-dimethyl-5 alpha-cholest-8,24-diene-3 beta- ol) from bull testicular tissue. Quite unexpected, these two sterols, which introduce the cholesterol biosynthetic pathway from lanosterol, may be loc ally acting substances with important physiological function for reproducti on. FF-MAS and T-MAS are present in the preovulatory follicular fluid of di fferent mammalian species and have the capacity to initiate resumption of m eiosis in mouse oocyte cultured in the presence of hypoxanthine, a natural meiosis maturation inhibitor. FF-MAS is produced by the cumulus cells of in tact oocyte-cumulus complexes upon FSH-stimulation and provides the oocyte with a go-signal for the resumption of meiosis. T-MAS constitutes the vast majority of MAS found in the mammalian testis and in the human ejaculate; i n particular a high concentration is found in the spermatozoa. T-MAS may be produced by the spermatids and the presence of T-MAS in spermatozoa may su ggest that T-MAS plays a role in fertilization by affecting the second meio tic division. (C) 1999 Wiley-Liss,Inc.