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 Summary The retrotransposon R2 initiates restoration of ribosomal DNA copies to trans-generationally maintain essential locus.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Revision includes additional experiments demonstrating the RNAi activity, as well as includes the use of an additional RNAi line. Revision also includes experiments confirming the heritability of rDNA copy number expansions.