Evolutionary dynamics of glue gene copy number in Drosophila species

Abstract

Background During evolution, genes can experience duplications, losses, inversions and gene conversions. Why certain genes are more dynamic than others is poorly understood. Here we examine how several Sgs genes encoding glue proteins, which make up a bioadhesive that sticks the animal during metamorphosis, have evolved in Drosophila species. Results We examined high-quality genome assemblies of 24 Drosophila species to study the evolutionary dynamics of the Sgs1-Sgs3-Sgs7-Sgs8 family glue genes at an unprecedented resolution across approximately 30 millions of years. A total of 102 Sgs genes were annotated and grouped into 4 subfamilies. We present here a new nomenclature for Sgs genes based on protein sequence conservation, genomic location and presence/absence of internal repeats. Two types of glue genes were uncovered. The first category (Sgs1, Sgs3X, Sgs3e) experienced a few gene losses but no duplication, no local inversion and no gene conversion. The second group (Sgs3b, Sgs7, Sgs8) exhibited multiple events of gene losses, gene duplications, local inversions and gene conversions. Our data suggest that the presence of short "new glue" genes near the genes of the latter group may have accelerated their dynamics. Conclusions Our comparative analysis suggests that the evolutionary dynamics of glue genes is influenced by genomic context. Our molecular, phylogenetic and comparative analysis of the glue gene family Sgs1-Sgs3-Sgs7-Sgs8 provides the foundation for investigating the role of the various glue genes during Drosophila life.