High-throughput analysis of satellite DNA in the grasshopper Pyrgomorpha conica reveals abundance of homologous and heterologous higher-order repeats

Satellite DNA (satDNA) constitutes an important fraction of repetitive DNA in eukaryotic genomes, but it is barely known in most species. The high-throughput analysis of satDNA in the grasshopper Pyrgomorpha conica revealed 87 satDNA variants grouped into 76 different families, representing 9.4% of the genome. Fluorescent in situ hybridization (FISH) analysis of the 38 most abundant satDNA families revealed four different patterns of chromosome distribution. Homology search between the 76 satDNA families showed the existence of 15 superfamilies, each including two or more families, with the most abundant superfamily representing more than 80% of all satDNA found in this species. This also revealed the presence of two types of higher-order repeats (HORs), one showing internal homologous subrepeats, as conventional HORs, and an additional type showing non-homologous internal subrepeats, the latter arising by the combination of a given satDNA family with a non-annotated sequence, or with telomeric DNA. Interestingly, the heterologous subrepeats included in these HORs showed higher divergence within the HOR than outside it, suggesting that heterologous HORs show poor homogenization, in high contrast with conventional (homologous) HORs. Finally, heterologous HORs can show high differences in divergence between their constituent subrepeats, suggesting the possibility of regional homogenization.