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Transport and disassembly of adhesion junctions in the testis Guttman, Julian Andrew

Abstract

The cytoskeleton and its associated proteins are involved with numerous cellular activities including intracellular transport, maintenance of cell integrity, and strengthening intercellular junctional attachment. During sperm production, the seminiferous epithelium of the mammalian testis undergoes numerous cyclical changes, which involve cytoskeletal events. This epithelium is composed of the spermatogenic cells and their nurse cells, the Sertoli cells. Intercellular attachment between adjacent Sertoli cells as well as Sertoli cells and the maturing spermatids occurs through specialized actin-rich adhesion junction plaques found within Sertoli cells, termed ectoplasmic specializations. Throughout spermatid maturation, dynamic cytoskeletalrelated processes lead to the transport of Sertoli/spermatid associated ectoplasmic specializations along Sertoli cell microtubules. This is followed by junction disassembly at Sertoli/spermatid regions during sperm release and junction turnover at Sertoli/Sertoli sites to allow the next generation of spermatogenic cells into the adluminal compartment of the epithelium. Studying the mechanisms by which these junction plaques are transported and disassembled will increase our knowledge of the processes occurring during spermatid transport within the seminiferous epithelium and spermatid release. In chapter 2, of this thesis I present the first evidence that a kinesin is associated with ectoplasmic specializations and identify two kinesin isoforms potentially involved in the entrenchment of spermatids within the seminiferous epithelium. In chapter 3, I demonstrate that the actin severing and capping protein, gelsolin, is a component of ectoplasmic specializations and show the first evidence that gelsolin may play a role in actin plaque disassembly. In chapter 4, I show that gelsolin and the small GTPase upstream regulator of gelsolin, Racl , are both present at ectoplasmic specialization locations throughout spermiogenesis. In chapter 5, I demonstrate that ectoplasmic specialization components are present at tubulobulbar complexes and give the first evidence that tubulobulbar complexes are involved in the internalization of ectoplasmic specialization membrane associated components. In chapter 6, I show that the actin disassembly factor, non-muscle cofilin, is found at tubulobulbar complexes and not at ectoplasmic specializations. These findings, united around the theme of adhesion junction transport and disassembly in the testis, significantly increase our understanding of the molecular events occurring during spermatid entrenchment and release in the seminiferous epithelium.

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