Lanosterol 14 alpha-demethylase (CYP51), NADPH-cytochrome P450 reductase and squalene synthase in spermatogenesis: late spermatids of the rat expressproteins needed to synthesize follicular fluid meiosis activating sterol

Lanosterol 14 alpha-demethylase (CYP51) is a cytochrome P450 enzyme involve d primarily in cholesterol biosynthesis. CYP51 in the presence of NADPH-cyt ochrome P450 reductase converts lanosterol to follicular fluid meiosis acti vating sterol (FF-MAS), an intermediate of cholesterol biosynthesis which a ccumulates in gonads and has an additional function as oocyte meiosis-activ ating substance. This work shows for the first time that cholesterogenic en zymes are highly expressed only in distinct stages of spermatogenesis. CYP5 1, NADPH-P450 reductase (the electron transferring enzyme needed for CYP51 activity) and squalene synthase (an enzyme preceding CYP51 in the pathway) proteins have been studied. CYP51 was detected in step 3-19 spermatids, wit h large amounts in the cytoplasm/residual bodies of step 19 spermatids, whe re P450 reductase was also observed. Squalene synthase was immunodetected i n step 2-15 spermatids of the rat, indicating that squalene synthase and CY P51 proteins are not equally expressed in same stages of spermatogenesis. D iscordant expression of cholesterogenic genes may be a more general mechani sm leading to transient accumulation of pathway intermediates in spermatoge nesis. This study provides the first evidence that step 19 spermatids and r esidual bodies of the rat testis have the capacity to produce MAS sterols i n situ.