SITE OF ACTIN FIBER DEPOLYMERIZATION WITHIN RAT SERTORI CELLS AS DETECTED BY LOCALIZATION OF BETA-THYMOSIN

The localization of actin sequestering peptide thymosin beta 10 in rat testis was analyzed by light and electron microscopic immunohistochem istry using the anti-thymosin beta 10 antibody. A positive reaction of thymosin beta 10 was detected in a closely associated portion within the developing spermatid head. In step 15 spermatids, localized deep i n the seminiferous epithelium, a prominent positive reaction was detec ted in the Sertoli cell cytoplasm adjacent to the spermatids. In step 19 spermatids, just before spermiation, thymosin beta 10 was highly co ncentrated in the Sertoli cell cytoplasm situated at the concave side of the sickle shaped spermatid head, where the tubulobulbar complex is formed. According to previous ultrastructural observations, actin bun dles of ectoplasmic specialization change to electron dense material j ust prior to spermiation. The localization of thymosin beta 10 suggest s that large amounts of actin monomers accumulate in the region of the tubulobulbar complex just prior to spermiation. These findings sugges t that thymosin beta 10 accumulation is correlated with fragmentation of the ectoplasmic specialization, and strongly support the hypothesis that the tubulobulbar complex is an actin-disorganizing organelle of the Sertoli cell.