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Abstract
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.
Highlights
Spermatogenic process is divided largely into three phases: 1) the proliferative phase in which spermatogonia undergo rapid successive division, 2) the meiotic phase in which recombination and segregation of chromosomes occur, 3) the differentiation phase in which spermatids transform drastically into spermatozoa which are motile cells carrying haploid genome to the egg [1,2]
The results clearly show that these two signals are present in the tubulobulbar complexes (TBC), suggesting the ubiquitin-proteasome system participates in the degradation of unnecessary proteins in the head cytoplasm of late
The sickle-shaped heads of very late spermatids were embedded in an apical process of the Sertoli cell cytoplasm which widely spread in the ventral side but not in the dorsal side of the spermatid head
Summary
Spermatogenic process is divided largely into three phases: 1) the proliferative phase in which spermatogonia undergo rapid successive division, 2) the meiotic phase in which recombination and segregation of chromosomes occur, 3) the differentiation phase in which spermatids transform drastically into spermatozoa which are motile cells carrying haploid genome to the egg [1,2]. Spermatids transform to sperm which are released into the lumen of seminiferous tubule. This process, spermiation, is composed of a series of complicated phenomena in which Sertoli cells deeply involve [11,12,13]. The tubular processes extend in the cytoplasm of Sertoli cell and their apex distends to form globule (bulbus) which assembles each other. They called the structure “tubulobulbar complexes” and supposed that the structures function as a scaffold to anchor the spermatid head to the Sertoli cell [14]. The activity of acid phosphatase, a lysosomal marker enzyme, was detected in the TBC and in the cytoplasm of Sertoli cell surrounding the bulbi, suggesting that the lysosomal degradation system is involved in the elimination of cytoplasm from the head region of late spermatid [16]
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