The retrotransposon R2 maintains Drosophila ribosomal DNA repeats

Abstract

Ribosomal DNA (rDNA) loci contain the hundreds of tandemly repeated copies of ribosomal RNA genes needed to support cellular viability. This repetitiveness makes it highly susceptible to copy number (CN) loss, threatening multi-generational maintenance of rDNA. How this threat is counteracted to avoid extinction of the lineage has remained unclear. Here, we show that the rDNA-specific retrotransposon R2 is essential for rDNA CN maintenance in the Drosophila male germline, despite the perceived disruptive nature of transposable elements. Depletion of R2 led to defective rDNA CN maintenance, causing a decline in fecundity over generations and eventual extinction. This study reveals that active retrotransposons can provide a benefit to their hosts, contrary to their reputation as genomic parasites, which may contribute to their widespread success throughout taxa. One Sentence SummaryThe retrotransposon R2 initiates restoration of ribosomal DNA copies to trans-generationally maintain essential locus.