Silencing and reactivation of rRNA genes in Drosophila

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Fruit fly, Drosophila melanogaster, is a premier model to study how some parasitic genes copy themselves into the new sites in the chromosomes, spreading around the genome, and how living species counteract these parasites. Ribosome, the most important molecular machine in the cell, is encoded by several hundred genes in fruit fly, and some of these genes are suffering from the invasion of genetic parasites, known as R1 and R2 retrotransposons. The cells have a way of turning these genes off, but under some stress conditions, these inserted genes are turned back on. The proposed study will examine the mechanisms by which these genes switch from silent to active form. Social impacts of this project will introduce basic concepts in genetics and cell biology to underrepresented students in area middle and high schools, provide an opportunity for hands-on research training for underrepresented high school students and undergraduates, and train graduate students in advanced genetics and cell biology. This project will also ensure continued research training for underrepresented undergraduate and graduate students at Louisiana State University. There are ~400 ribosomal RNA gene clusters in Drosophila melanogaster, and ~60% of them contain insertions of R1 and/or R2 retrotransposons. R2 elements naturally reside within the 28S region of approximately 16% of the rRNA genes in Drosophila. These inserted genes are normally silent and are considered heterochromatic, while the remaining active non-inserted copies provide the required amount of rRNA for the cell needs. Previous results showed that R2 elements are transcribed upon nucleolar stress caused by the loss of the nucleolar ribosome assembly factor, Nopp140. This project examines the putative conversion of the rRNA genes with inserted R2 retrotransposons from a silent heterochromatic state to an active euchromatic state upon nucleolar stress. The key question that will be answered is whether de-repressed R2 is co-linearly expressed with extra 28S rRNA by Pol I, or excess enhanced R2 expression is independent of additional rDNA unit expression. This project will introduce basic concepts in genetics and cell biology to students from cohorts underrepresented in STEM in the Baton Rouge area middle and high schools, provide an opportunity for hands-on research training for underrepresented high school students and undergraduates, and train graduate students as well as high school teacher in advanced genetics and cell biology. Out-reach efforts will include middle and high schools in Scotlandville - a distressed, predominantly African-American neighborhood. Assessment of middle, high school, and undergraduate training will employ pre-, formative, and summative.