Fig. 1.

Postlanosterol intermediates of cholesterol synthesis. Mouse genes encoding enzymes that catalyze individual enzymatic steps are displayed in red or blue. Sites of enzymatic changes in individual sterol intermediates are displayed with arrows. Note the up-regulation of Cyp51 and down-regulation of postMAS genes Sc4mol and Dhcr7 reported during development of the rat testis (a) (9). Discordant regulation of cholesterogenic enzymes is a possible reason for the accumulation of T-MAS in the testis of rat (a), guinea pig (b) (12), and mouse (c) (13), compared with the quantity of T-MAS in the liver. Three-dimensional structures of lanosterol, FF-MAS, desmosterol, and cholesterol obtained with a Pc3D molecule viewer display the spatial conformation of individual intermediates, which might affect sperm membrane properties.