Gelsolin--evidence for a Role in Turnover of Junction-related Actin Filaments in Sertoli Cells

The gelsolin-phosphoinositide pathway may be part of the normal mechanism by which Sertoli cells regulate sperm release and turnover of the blood-testis barrier. The intercellular adhesion complexes (ectoplasmic specializations) involved with these two processes are tripartite structures consisting of the plasma membrane, a layer of actin filaments and a cistern of endoplasmic reticulum. Gelsolin is concentrated in these adhesion complexes. In addition, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) and phosphoinositide-specific phospholipase C are found in the structures. Treatment of isolated spermatid/junction complexes with exogenous phosphoinositide-specific phospholipase C, or with a synthetic peptide consisting of the PtdIns(4,5)P(2) binding region of gelsolin, results in the release of gelsolin and loss of actin from the adhesion complexes. We present a model for the disassembly of the actin layer of the adhesion complex that involves the hydrolysis of PtdIns(4,5)P(2) resulting in the release of gelsolin within the plaque. Further, we speculate that the hydrolysis of PtdIns(4,5)P(2) may result in a local Ca(2+) surge via the action of inositol triphosphate on junctional endoplasmic reticulum. This Ca(2+) surge would facilitate the actin severing function of gelsolin within the adhesion complex.