Testing the Effects of Fast-Evolving Heterochromatic Genes on Euchromatic Transposable Elements in Drosophila
Authors: Leila Lin; Yuh Chwen G. Lee
Affiliation: UC Irvine
Keywords: a. genome evolution; s. other organisms
Eukaryotic genomes consist of gene-rich, transcriptionally active euchromatin and gene-poor, silenced heterochromatin. The tightly packed heterochromatic regions make up at least 20% of the human genome and about one-third of the fruit fly (Drosophila) genome. Heterochromatic genes play a central role in maintaining the stability of the genome. Specifically, their protein products are involved in the epigenetic silencing and compartmentalization of repetitive sequences and transposable elements (TE) that are enriched in heterochromatin. Accordingly, we hypothesize that heterochromatic genes must be fast evolving in order to keep up with the rapidly-changing and oftentimes deleterious repetitive sequences and transposable elements in heterochromatin. Supporting this hypothesis, we have identified fast-evolving heterochromatic genes across sixteen species of Drosophila flies. We achieved this through performing copy number variation analysis, a phylogenetic analysis by maximum likelihood (PAML) to test evolution across long evolutionary time, and a McDonald-Kreitman test (MK) to test evolution across short evolutionary time. To test whether the fast evolution of these heterochromatic genes may also influence euchromatic TEs that are epigenetically silenced with enrichment of heterochromatic marks, we crossed flies with a mutation for the genes of interest to a reporter strain with red fluorescent marker next to with various families of TEs. Changes in the intensity of the fluorescence would provide information about the extent of epigenetic silencing of TEs in the euchromatic genome. Our study will connect how the fast-evolving gene-poor heterochromatin may shape the evolution of gene-rich euchromatin.