Access Type

Open Access Dissertation

Date of Award

January 2023

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

Victoria H. Meller

Abstract

Drosophila melanogaster males have one X chromosome while females have two. This creates an imbalance in X:A gene dosage between the sexes. This imbalance is corrected by increasing transcription of male X-linked genes approximately two-fold. This process involves the Male Specific Lethal (MSL) complex, which is recruited to Chromatin Entry Sites (CES) and transcribed X-linked genes where it modifies chromatin to increase expression. It is unclear how the MSL complex recognizes X-chromatin. Repetitive sequences strikingly enriched in X euchromatin, the 1.688X satellite repeats, also promote recruitment of the MSL complex to nearby genes. Unlike CES, the 1.688X repeats do not recruit the MSL complex directly. The genetic architecture of recruitment by these DNA elements repeats remains speculative. To facilitate dissection of the mechanism of recruitment, we developed a luciferase reporter system for recruitment of compensation to an autosome. We discovered that the promoter driving luciferase is critical. Upon testing Actin 5C, Hsp83 and Dmn promoters, we found that only the Dmn-driven reporter responded as expected to the presence of recruiting elements. In contrast, Actin 5C and Hsp83 promoters appear able to recruit compensation by themselves, and expression is not further enhanced by the addition of recruiting elements. The system was validated by knock down of genes known to participate in compensation. Knock down of factors genetically linked to X recognition reveal that 1.688X repeats recruit through a different mechanism than the CES. Our findings suggest that 1.688X repeats play a larger role during embryogenesis, whereas the contribution of 1.688X repeats and CES is equivalent later in development. Our studies also reveal unexpected complexity and potential interdependence of recruiting elements.

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