Further observations on tubulobulbar complexes formed by late spermatids and sertoli cells in the rat testis

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Abstract
The present study extends earlier findings (Russell and Cler‐mont, '76) by describing additional details of the structure, relationships, distribution, origin, and fate of tubulobulbar complexes. Freeze‐fracture and thin section observations reveal few membrane associated particles and no appreciable cell coat in the membranes forming the tubulobulbar complex. The opposing plasma membranes of the complex do not appear to form a junction, although junctional formation might be expected by the close proximity (4.0 nm apart) of the Sertoli and spermatid plasma membranes. Sertoli filaments of the network which encircle the tubular portion of the complex measure 5.0‐7.0 nm across and appear to insert into the Sertoli plasma membrane. Tubulobulbar complexes initially form in association with a cell surface modification (bristle‐coated pit) of the Sertoli plasma membrane. The first tubulobulbar complexes develop large bulbous components (up to 2.5μm across), which soon lose connection with the spermatid and become incorporated into large phagocytic vacuoles (secondary lysosomes). As bulbs undergo dissolution, newly formed tubulobulbar complexes are observed to replace these structures. Thus, the data indicate that more than one generation of tubulobulbar complexes develop. Moreover, the tubular and bulbous portions of most dissociating complexes (as well as neighboring Sertoli lysosomes) show acid phosphatase activity. Near the time of sperm release, all complexes at the concave aspect of the spermatid head are resorbed. New tubulobulbar complexes, many lacking terminal bulbous dilations, form at the dorsal and lateral aspects of the spermatid head. These persist even after all ectoplasmic specializations and most Sertoli cytoplasm have been withdrawn from a position facing the spermatid head. The presence of tubulobulbar complexes just prior to the time of sperm release is in support of previous findings indicating that tubulobulbar complexes participate in anchoring the head of the late spermatid prior to sperm release. Past the zone of sperm release a few abnormally shaped cells, which had not been released with other spermatids of the same generation, display intact tubulo‐bulbar complexes. The persistence of these and other structures may be the means by which abnormally shaped spermatids are retained and prevented from traversing the male duct system.