Investigation Of X Chromosome Recognition: The Role Of Small Rna In Drosophila Dosage Compensation

<p>In humans and flies, females have two X chromosomes but males have one X chromosome and one Y chromosome. This leads to a fatal imbalance in X-linked gene expression in one sex. In mammals and in the fruit fly <i>Drosophila</i>, modulation of X chromosome expression is critical for survival. This process is termed dosage compensation. Flies increase expression from the male X chromosome two-fold. This is achieved by the Male Specific Lethal (MSL) complex, which consists of two large, non-coding RNA on the X transcripts (<i>roX1</i> and <i>roX2</i>) and five proteins. The roX RNAs have a critical role in complex localization to the X chromosome. Simultaneous mutation of <i>roX1</i> and <i>roX2</i> reduces X localization of the MSL proteins, lowers X-linked expression and reduces male survival. Using <i>roX1 roX2</i> mutants, we performed genetic studies to identify modifiers of X chromosome recognition. In spite of a lack of expression in somatic tissues, the Y chromosome is a potent modifier of the <i>roX1 roX2</i> phenotype. I postulated that the Y chromosome could affect dosage compensation through a small RNA-dependent pathway, and performed a screen of RNAi mutations. This screen identified four siRNA genes that, when mutated, enhance <i>roX1 roX2</i> male lethality and disrupt MSL localization to the X chromosome. The role of the siRNA pathway in dosage compensation prompted an investigation of potential sources of siRNA. A class of 1.688g/cm3 satellite-related repeats is exclusive to the X chromosome (1.688^X). These are transcribed, and thus capable of generating siRNA in animals. Ectopic expression of long single stranded 1.688^X RNA reduced roX1 roX2 male survival. In contrast, expression of double stranded 1.688^X hairpin RNA produced high levels of corresponding small RNA and dramatically rescued roX1 roX2 male survival. MSL localization to the X chromosome was partially restored in flies expressing 1.688^X hairpin RNA. Rescue of <i>roX1 roX2</i> males was dependent upon the siRNA genes Dcr2 and Ago2. These studies reveal that small RNA from X-linked repeats acts through the siRNA pathway to promote X chromosome recognition. I postulate that the 1.688^X RNA repeats underline X chromosome identity. Future studies exploring this process will help us to understand the molecular basis for exclusive modification of the X chromosome.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Open Access Dissertation

Discipline thesis:degree_discipline

Biological Sciences

Year dc:date.available

2013

Author dc:creator

• Menon, Debashish Unnikrishnan

Contributors dc:contributor

• Victoria H. Meller

• Dosage compensation
• Imprinting
• non coding RNA
• small RNA
• Biology
• Genetics
• Molecular Biology

Repository record dc:identifier

https://digitalcommons.wayne.edu/oa_dissertations/672

OAI identifier oai:identifier

oai:digitalcommons.wayne.edu:oa_dissertations-1671