Distinct satellite DNA composition between core and germline restricted chromosomes in Bradysia (Sciara) coprophila

Abstract

Programmed DNA elimination (PDE), a phenomenon wherein cells eliminate a subset of genetic material during certain stages of development, is observed in a broad range of organisms. The fungus gnat Bradysia (formerly Sciara) coprophila undergoes a series of PDE events during their development, including elimination of germline-restricted chromosomes (called L chromosomes) in soma and elimination of paternal chromosomes during male meiosis. However, the underlying mechanisms of this phenomenon are poorly understood. Highly repetitive satellite DNA, which often shows chromosome specific distribution, is a possible candidate for sequences involved in PDE. In this study, we utilized recent genomic data and genome assemblies to identify new satellite DNA sequences of B. coprophila. Through characterization of satellite DNA distribution on chromosomes, we found that the X and autosomes do not share centromeric satellite DNA sequence with the L chromosomes. We further provide the cytological evidence that confirms a recent finding based on the genome assembly that there are two distinct L chromosomes that were not previously distinguished cytologically. Together, our work lays a foundation for future studies to explore the possible connection between satellite DNA and the mechanism of PDE in B. coprophila.