Cross-species incompatibility between a DNA satellite and the Drosophila Spartan homolog poisons germline genome integrity

Abstract

ABSTRACTSatellite DNA spans megabases of eukaryotic sequence and evolves rapidly. Paradoxically, satellite-rich genomic regions mediate strictly conserved, essential processes like chromosome segregation and nuclear structure. A leading resolution to this paradox posits that satellite DNA and satellite-associated chromosomal proteins coevolve to preserve these essential functions. We experimentally test this model of intra-genomic coevolution by conducting the first evolution-guided manipulation of both chromosomal protein and DNA satellite. The 359bp satellite spans an 11Mb array in D. melanogaster that is absent from its sister species, D. simulans. This species-specific DNA satellite colocalizes with the adaptively evolving, ovary-enriched protein, Maternal Haploid (MH)–the Drosophila homolog of Spartan. To determine if MH and 359 coevolve, we swapped the D. simulans version of MH (“MH[sim]”) into D. melanogaster. MH[sim] triggers ovarian cell death, reduced ovary size, and loss of mature eggs. Surprisingly, the D. melanogaster mh null mutant has no such ovary phenotypes, suggesting that MH[sim] is toxic in a D. melanogaster background. Using both cell biology and genetics, we discovered that MH[sim] poisons oogenesis through a DNA damage pathway. Remarkably, deleting the D. melanogaster-specific 359 satellite array completely restores mh[sim] germline genome integrity and fertility, consistent with a history of coevolution between these two fast-evolving loci. Germline genome integrity and fertility are also restored by overexpressing Topoisomerase II (Top2), suggesting that MH[sim] interferes with Top2-mediated processing of 359. The observed 359-MH[sim] cross-species incompatibility supports a model under which ostensibly inert repetitive DNA and essential chromosomal proteins must coevolve to preserve germline genome integrity.