Date of Award

Spring 4-15-2016

Degree Type

Thesis

Degree Name

MS Biology

Department

Biology

Advisor

Angela Klaus, Ph.D

Committee Member

Brian Nichols, Ph.D

Committee Member

Tin-Chun Chu, Ph.D

Committee Member

Jane L. Ko, Ph.D

Keywords

Stem cell niche, Spermatogenesis, Drosophila, cadmium

Abstract

The fruit fly Drosophila melanogaster is used extensively as a model for studying molecular, genetic and cellular aspects of human disease and physiology. Our lab has used D. melanogaster and related species to study the structure of the testis stem cell niche, as well as other aspects of spermatogenesis. We previously revealed a novel stem cell niche structure in D. pseudoobscura, a distant relative of D. melanogaster. The signaling center of the D. melanogaster stem cell niche has a well-characterized rosette arrangement of fasciclin-positive cells terms the “hub”. D. pseudoobscura, however, lacks a punctuate hub and instead displays a hemispherical fasciclin-positive zone that fills the apical end of the testis. The first aim of the current work was to characterize the stem cell niche in two additional species based on their evolutionary relationship to D. melanogaster and D. pseudoobscura: D. ananassae and D. persimilis. D. persimilis is part of the obscura group and is closely related to D. pseudoobscura; D. ananassae is part of the melanogaster group. Our work shows that D. ananassae has the rosette hub morphology while D. persiimilis displays the D. pseudoobscura morphology.

The second focus of this project was to examine the effects of cadmium (CdCl2) exposure on spermatogenesis in D. melanogaster. Cadmium toxicity is well-studied in mammalian testes and sperm production, but not in Drosophila. In order to assess the effects of CdCl2 on spermatogenesis in D. melanogaster we developed two assays: a nuclear staining (DAPI) assay to assess cadmium dosage effects on late spermiogenesis and a Live/Dead assay to assess mature sperm viability. The results of the DAPI assay and the Live/Dead assay both show a detrimental effect by CdCl 2 on spermatogenesis in D. melanogaster. The goal of the DAPI assay was to examine the number and arrangement of sperm bundles in the basal end of the D. melanogaster testis following cadmium treatment. The DAPI assay showed that exposure to increasing concentration of CdCl2 resulted in an increase in the appearance of abnormal sperm bundles. The Live/Dead assay showed: (1) an increase in the total number of sperm present in the seminal vesicle proportional to increasing amounts of cadmium chloride and (2) an increase in the number of dead sperm proportional to increasing amounts of cadmium chloride.

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