Fine structure of the formation and fate of the residual bodies of mouse spermatozoa with evidence for the participation of lysosomes

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Abstract
Routine electron microscopy in combination with subcellular localization of acid phosphatase has been employed to study the formation and fate of residual cytoplasmic bodies extruded into the tubular lumen shortly before spermiation. Prior to extrusion the spermatid cytoplasm contains lipid droplets, mitochondria, ribosomes, endoplasmic reticulum, the caudally migrated Golgi apparatus, and numerous multivesicular and multigranular bodies. These membrane‐limited bodies and the Golgi zone stain heavily for acid phosphatase. Following extrusion the residual bodies undergo a series of alterations: (1) disruption of multigranular bodies with release of free granules; (2) sequestration of granules, ribosomes, and reticulum inside double‐membrane‐limited vacuoles derived from Golgi lamellae; (3) appearance of numerous, single‐membrane‐bound, cytoplasmic vacuoles; (4) fragmentation; (5) peripheral migration toward the tubular wall; and (6) phagocytosis of these migrating fragments by the Sertoli cells. The demonstration of acid phosphatase activity within free granules, the sequestering Golgi lamellae, and both classes of vacuoles suggests that initial residual body degradation occurs through lysosomal cytoplasmic autophagy.