Peroxisomes and ether lipid biosynthesis in rat testis and epididymis

Plasmalogens are a main component of the spermatozoon membrane, playing a c rucial role in their maturation. The initial steps in plasmalogen biosynthe sis are catalyzed by two peroxisomal enzymes, dihydroxyacetonephosphate acy ltransferase and alkyl-dihydroxyacetonephosphate synthase, The localization of both enzymes in the membrane of peroxisomes implies that plasmalogen-pr oducing cells should contain this organelle. To unravel the putative source of spermatozoan plasmalogens we investigated which cell types in the testi s and epididymis are endowed with peroxisomes. To this extent, testicular a nd epididymal tissue was analyzed at the protein and RNA levels by means of light and electron microscopical immunocytochemistry as well as by Western and Northern blotting. Proteins and mRNAs of peroxisomal enzymes, especial ly those of dihydroxyacetonephosphate acyltransferase and alkyl-dihydroxyac etonephosphate synthase, were detected in the testis and epididymis. In the testis, peroxisomes were localized exclusively in Leydig cells and not in cells of the seminiferous tubules, implying that the latter do not contribu te to the biosynthesis of plasmalogens of the sperm membrane. In contrast, peroxisomes could be clearly visualized in the epithelial cells of the epid idymis. The results suggest that peroxisomes in epithelial cells of the rat epididymis play a pivotal role in the biosynthesis of plasmalogens destine d for delivery to the sperm plasma membrane.