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Access Type
WSU Access
Date of Award
January 2024
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Biological Sciences
First Advisor
Victoria V. Meller
Abstract
Organisms with differentiated sex chromosomes must accommodate unequal gene dosage in males and females. Male fruit flies increase X-linked gene expression to compensate for hemizygosity of the single X chromosome. Full compensation requires localization of the Male-Specific Lethal (MSL) complex to active genes on the male X, where it modulates chromatin to elevate expression. The mechanisms that identify X chromatin are poorly understood. The euchromatic X is enriched for AT-rich, ~359 bp satellites termed the 1.688X repeats. Autosomal insertions of 1.688X DNA enable MSL recruitment to nearby genes. Ectopic expression of dsRNA from one of these repeats produces siRNA and partially restores X-localization of MSLs in males with defective X recognition. Surprisingly, expression of double stranded RNA from three other 1.688X repeats failed to rescue males. We reconstructed dsRNA-expressing transgenes with sequence from two of these repeats and identified phasing of repeat DNA, rather than sequence or orientation, as the factor that determines rescue of males with defective X recognition. Small RNA sequencing revealed that siRNA was produced in flies with transgene that rescues, but not in those carrying a transgene with identical sequence and different phasing. We demonstrate that closely related repeats in pericentromeric X heterochromatin promote X-recognition through a maternal effect, potentially mediated by small RNA, suggesting that the sources of siRNAs that promote X recognition are highly redundant. We propose that enrichment of satellite repeats on Drosophilid X chromosomes facilitates the rapid evolution of differentiated sex chromosomes by marking the X for compensation.
Recommended Citation
Biswas, Sudeshna, "Widespread X Chromosome Repeats Play A Central Role In Drosophila Melanogaster X Chromosome Recognition" (2024). Wayne State University Dissertations. 3967.
https://digitalcommons.wayne.edu/oa_dissertations/3967
