REGULATION OF THE SECRETION AND SYNTHESIS OF RAT SERTOLI-CELL SGP-1, SGP-2 AND CP-2 BY ELONGATE SPERMATIDS

The aim of this study was to investigate the effect of the absence of elongate spermatids (ES) from the rat seminiferous epithelium on the q uantitative secretion and synthesis of the three major Sertoli cell se cretory proteins - SGP-1, SGP-2 and CP-2. Seminiferous tubules (ST) we re isolated (a) from normal 28-day-old rats, in which the most mature germ cell type is the round spermatid, (b) from normal adult rats at s tages IX-XIV of the spermatogenic cycle, i.e. after spermiation, or at stages I-V and VI-VIII, when ES are still attached to the Sertoli cel l, and (c) at stages VI-VIII from normal adult rats and from rats trea ted with methoxyacetic acid (MAA) in order to specifically deplete ES at these stages. Two-dimensional SDS PAGE combined with computerized i mage analysis was used to analyse S-35-methionine-labelled intracellul ar and secreted proteins. In the case of SGP-1 and SGP-2, almost all o f the protein synthesized by ST was secreted. The total amount of both SGP-1 and CP-2 secreted by unstaged ST from immature rats was signifi cantly lower than that secreted by unstaged ST from adult rats. The to tal amount of SGP-1 and CP-2 secreted by-adult ST at stages IX-XIV of the spermatogenic cycle also declined dramatically compared to ST at e arlier stages. The proportion of the total CP-2 synthesized by ST whic h was secreted also declined in all situations in which ES were absent from the seminiferous epithelium. The synthesis of only SGP-2 was cha nged by ES depletion from ST at stages VI-VIII, which was almost doubl ed compared to synthesis of this protein by ST from control rats. Our results suggest strongly that the secretion of SGP-1 and SGP-2 is via the constitutive pathway, and that regulation of these two proteins by ES is at the level of protein synthesis. In contrast, the regulation of CP-2 by ES is predominantly at the level of secretion, suggesting t hat this protein is secreted via a regulated pathway. Our findings add to the evidence showing that ES play a major role in the regulation o f Sertoli cell function.