Lipid droplets in fractions enriched in spermatocytes, spermatids and residual bodies

Abstract

In seminiferous tubules, Sertoli cells play a chief role in providing structural and functional support to spermatogenesis. Those germ cells that cannot be supported are led into apoptosis and rapidly eliminated by phagocytosis. At their luminal pole, Sertoli cells also support spermiation: as spermatids are released from the seminiferous epithelium, residual bodies are rapidly engulfed and degraded in Sertoli cells. In this work we isolated cell fractions enriched in pachytene spermatocytes, spermatids, and residual bodies to study their lipids and fatty acids. None of the germ cell fractions contained cholesterol esters, confirming that within seminiferous tubules these lipids are exclusive of Sertoli cell droplets. Glycerophospholipids rich in 22:5n-6 and sphingomyelin with 28:4n-6 and 32:5n-6 were more abundant in spermatocytes and especially in spermatids than in residual bodies. In contrast, the latter contained the highest proportion of 22:5-rich triglycerides of the three fractions. When Nile Red was used as a marker of oil droplets, spermatocytes and spermatids stained faintly and residual bodies fluoresced strongly and punctuated, indicating that 22:5- rich triglycerides were the main components of lipid droplets located within these structures. In vivo, recycling of residual body constituents including lipids and fatty acids may be one of the duties of Sertoli cells