Graduation Year

2017

Date of Submission

4-2017

Document Type

Open Access Senior Thesis

Degree Name

Bachelor of Arts

Department

W.M. Keck Science Department

Second Department

Biology

Reader 1

Patrick Ferree

Reader 2

Jennifer Armstrong

Rights Information

© 2017 Becky L Cheng

Abstract

Drosophila melanogaster and many other insects harbor intracellular bacterial symbionts that are transmitted vertically from infected host mothers to their offspring. Many of these bacteria alter host reproductive developmental processes in order to increase their transmission success. For example, Spiroplasma, a spirochete that naturally infects D. melanogaster, selectively kills males during mid-embryogenesis while sparing females. Previous studies suggested that Spiroplasma interacts genetically with the male-specific dosage compensation pathway, which causes ~2-fold up-regulation of most genes located on the male’s single X chromosome so that their expression matches the levels found in females who have two Xs. To further test this idea, I used confocal microscopy to visualize dosage compensation complex (DCC) localization and activity in infected as well as uninfected embryos. In the presence of Spiroplasma, the DCC became abnormally mis-localized across the nucleus. This pattern was accompanied by abnormal acetylation of histone H4K16, a mark induced by DCC activity and needed for proper X chromatin remodeling. My results imply that Spiroplasma directly targets the DCC by misdirecting it to uncompensated regions of the genome, an effect that leads to abnormal gene mis-regulation and consequent lethality (work from other members in our group). To further investigate this interaction, we transgenically expressed low levels of MSL-2 in both Spiroplasma infected and uninfected embryos in order to cause ectopic formation of the DCC in the female sex. I found that when infected, female embryos expressing the DCC showed significantly reduced viability in comparison to uninfected transgenic females. This result supports the notion that Spiroplasma uses the DCC in a dominant gain-of-function manner to kill embryos.

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