Differential fate of mitochondria during spermiogenesis in the ratfish Hydrolagus

During spermiogenesis in the ratfish Hydrolagus colliei, spermatid mitochondria follow one of three fates. Some are retained as functional spermatozoan mitochondria clustered in the midpiece, some are enclosed in large vacuoles and phagocytosed by Sertoli cells, and the remaining mitochondria are segregated to the remnant cytoplasm. In the latter site rhodamine 123 fluoresence studies show that the mitochondrial derivatives, although much altered morphologically, retain the electrochemical gradient characteristic of the inner mitochondrial membrane. Some mitochondrial derivatives show activity even after the remnant cytoplasm is cast off from the spermatozoon.