Graduation Year

2013

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

W.M. Keck Science Department

Second Department

Biology

Reader 1

Patrick M. Ferree

Reader 2

Zhaohua Irene Tang

Rights Information

© 2013 Jennifer Martin

Abstract

Bacteria living within the cells of eukaryotic organisms can have profound effects on their hosts. One example is host sex-ratio distortion caused by bacterial endosymbionts, which can be induced through the killing of male progeny during their development. The mechanisms that underlie how bacteria can cause male death are poorly understood. Several previous studies suggested that the neural, and perhaps other, tissues are targeted by the male-killing bacterium, Spiroplasma.In this study, I tested this hypothesis, addressing whether tissues were specifically altered during male development and also when the initial defects manifested. These questions were addressed by analyzing developing tissues ofinfected and uninfected embryos with immunological reagents and confocal microscopy. My analyses revealed that Spiroplasma causes severe cellular defects in the male central nervous system (CNS) during mid embryogenesis. Specific CNS defects include disrupted neuronal packing as they differentiate and highly abnormal axon formation, with both phenotypes occurring at 6 hours and worsening throughout embryo development. Additionally, my analyses showed that during the onset of these CNS defects, other tissue types appeared normal. However, during late embryonic stages, male embryos became highly abnormal in tissue morphology across the whole animal. These observations suggest that Spiroplasma initially targets the CNS, which may, in turn, lead to secondary widespread defects in male embryos. I propose important experiments focusing on analysis of neuronal precursors to further explore the cellular basis of male killing, and I offer a model for how male CNS tissue can be targeted specifically at the molecular level.

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