Priscilla Glenn

Document Type

Honors Thesis


The differentiation of sex chromosomes (eg. XY and ZW systems) has led to the chromosome-specific evolution of gene contents, rates of mutation and evolution, and specific forms of regulation including X-chromosome dosage compensation and meiotic sex chromosome inactivation (MSCI). MSCI has evolved independently within XY and XO systems and it is the process in which the unsynapsed sex chromosome(s) are silenced during meiosis in spermatogenesis. Within Drosophila, sex chromosome regulation is still unclear. Microarray analyses provide no evidence for MSCI but there is a significant chromosome-wide downregulation of X-linked gene expression that is established in premeiotic cells and persists into meiotic cells. The reduced expression cannot be explained by the absence of dosage compensation and suggests that a novel mechanism, termed X-Supression, limits X expression during spermatogenesis in Drosophila. Likewise, sex chromosome regulation is still unclear within Tribolium castaneum. Previous results based gene expression data from whole body males indicated that Xchromosome gene expression is compensated so that the X:AA ratio is ~1. To investigate whether dosage compensation also holds in male germline tissues we compare microarray data from whole body tissues and germline tissues of both sexes. We find that Xchromosome gene expression in male germline is significantly reduced compared to the autosomes and compared to the X chromosome in somatic tissues. X-chromosome gene expression in testes is consistent with a lack of dosage compensation because the X does not appear to be completely silenced as would be expected under MSCI. However, the modest expression levels may result from our samples consisting of a mixture of premeiotic, meiotic, and post-meiotic germline cells as well as contamination by a small number of somatic cells, thereby obscuring true MSCI. Resolving the extent to which Xlinked testes expression is governed by MSCI, lack of dosage compensation, or other mode of X-suppression awaits more fine scale analysis of cells at different stages of spermatogenesis.

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