Control of sperm quality in the epididymis by disintegration and removal – A transmission electron microscopy study of abnormal sperm of aflatoxin-treated rat

The mammalian epididymis is a dynamic organ endowed with diverse roles, including sperm quality control, which appears to occur during the epididymal processing and storage to prevent the misshapen spermatozoa from being present in the ejaculate in large numbers. This quality control mechanism is capable of identifying and removing dead/defective spermatozoa. In this respect, the role of a dense matrix arising from epididymal secretory aposomes/epididymosomes and associated disintegration/dissolution of dead/defective spermatozoa has been reported. This study was conceived to find if the mechanistic details of the disintegration of the parts of the spermatozoa along the length encompass the same or different patterns. We used photomicrographs from the experimental rat model induced into defective/unviable spermatozoa by aflatoxin B1 treatment. A meticulous screening of the matrix-embedded spermatozoa reflected different courses of disintegration of the major parts, namely, head, mid-piece, and flagellum. The disintegration of the head began with swelling of the acrosome and its lysis, followed by the gradual disintegration of the nucleus. In the mid-piece, the plasma membrane underwent disintegration first, and this was followed by disorganization and disintegration of the mitochondrial sheath and, subsequently, the outer dense fibers (ODFs). In the flagellum, neither the plasma membrane nor the fibrous sheath (FS) indicated any trace of disintegration initially. Rather, the FS and the plasma membrane were lifted off from the ODF-axoneme complex and, subsequently, with the FS remaining intact, the ODFs and the axonemal doublets on one side disintegrated, followed by disintegration of the remaining ODFs and the axonemal doublets. In the disintegration process, the spermatozoa’s head, mid-piece, and flagellum follow different courses, reflecting on the respective structural compositions.