Polyubiquitination and Proteasome Signals in Tubulobulbar Complexes of Rat Late Spermatids

To illustrate the involvement of tubulobulbar complexes (TBC) in ubiquitin-proteasome degradation of unnecessary proteins in the head cytoplasm of late spermatids, the localization of polyubiquitin and proteasome was studied by immunofluorescence and immunoelectron microscopy. Polyubiquitin localized to TBC and proteasome subunit α to dense materials surrounding the TBC in the cytoplasm of Sertoli cell enwrapping sickle-shaped spermatid heads. The results suggest that the TBC is a structural device for ubiquin-proteasome degradation of unnecessary proteins in the cytoplasm of spermatid head during rapid reduction of the head cytoplasm and nuclear compaction of late spermatids.

Localization of proteins involved in endocytosis at tubulobulbar complexes in rat testes

Tubulobulbar Complexes (TBCs) are actin-rich structures formed between Sertoli-cells and spermatids at the time of sperm release. The main functions of the TBCs are to remove excess spermatid cytoplasm and acrosomal contents, internalize and recycle junctional complexes by endocytosis prior to spermiation. However, in addition to recycling some of the molecules undergo lysosomal degradation. The molecular machinery involved in endocytosis at the TBCs is not well understood. To bridge this gap localization of various proteins, involved at various steps of endocytosis studied in other systems, was demonstrated in TBCs using testicular fragmented material or sections by immunoblotting and immunofluroscence. The presence of key molecules like Vamp-2, syntaxin and Lamp-2 indicates occurrence of lysosomal degradation in addition to junctional recycling at the TBCs present at the time of sperm release. TBCs are endocytic devices functioning to recycle junctional molecules or remove spermatid cytoplasm that were present between spermatids and Sertoli-cells all through the process of spermatid maturation and in turn regulate male fertility.