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Kinesin-based transport of ectoplasmic specializations and localization of dynamin 3 in the testis Vaid, Kuljeet S.

Abstract

The Sertoli cell cytoskeleton plays a number of roles including intracellular transport, maintenance of cell shape, and formation of adhesion junctions. During spermatogenesis, the cytoskeleton plays a number of roles to ensure the proper formation of spermatids in the seminiferous epithelium. The epithelium is composed of the spermatogenic cells as well as Sertoli cells. Sertoli cells act as nurse cells and provide support and nourishment to the developing spermatids. The spermatids are attached to Sertoli cells through actin-rich adhesion complexes known as ectoplasmic specializations. During spermatogenesis, these junctions and the associated spermatids are hypothesized to be transported along polarized microtubule tracts in the Sertoli cell to the base of the seminiferous epithelium before retreating back to the apex of the epithelial tissue. Upon reaching the apex of the tissue, the ectoplasmic specializations are disassembled and spermatids are released into the lumen of the seminiferous epithelium. The study of this junction transport and disassembly will help to better understand mechanisms of spermatogenesis. Recent work has provided evidence that a dynein motor protein is the likely mechanism which transports the spermatid/ectoplasmic specialization junction to the apex of the epithelium. In addition, past work using mRNA GeneChip data arrays has identified the Rab6KIFL kinesin to be highly expressed in Sertoli cells. In chapter 2 of this thesis, I present evidence that antibodies raised against the Rab6KIFL protein are associated with ectoplasmic specializations and that this motor may be involved in spermatid entrenchment. Results indicate localization of antibodies at ectoplasmic specializations at times of spermatogenesis when entrenchment occurs and localization of antibodies on the cytoplasmic face of ectoplasmic specializations. In chapter 3 of this thesis I demonstrate that dynamin 3 is present at tubulobulbar complexes and when transfected into eGFP-nectin-2y MDCK cells tube like structures form. Dynamin 3 is highly expressed in testis however its function has been unexplored. Here I demonstrate that dynamin 3 may facilitate formation of these structures. The findings summarized in this thesis are integrated around the predominant subject of adhesion junction transport and disassembly. This work provides insight into mechanisms involved in spermatid translocation and release during spermatogenesis.

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