Abstract
Rapid evolution of centromeric satellite repeats is thought to cause compensatory amino acid evolution in interacting centromere-associated kinetochore proteins. Cid, a protein that mediates kinetochore/centromere interactions, displays particularly high amino acid turnover. Rapid evolution of both Cid and centromeric satellite repeats led us to hypothesize that the apparent compensatory evolution may extend to interacting partners in the Condensin I complex (i.e., SMC2, SMC4, Cap-H, Cap-D2, and Cap-G) and HP1s. Missense mutations in these proteins often result in improper centromere formation and aberrant chromosome segregation, thus selection for maintained function and coevolution among proteins of the complex is likely strong. Here, we report evidence of rapid evolution and recurrent positive selection in seven centromere-associated proteins in species of the Drosophila melanogaster subgroup, and further postulate that positive selection on these proteins could be a result of centromere drive and compensatory changes, with kinetochore proteins competing for optimal spindle attachment.
Highlights
Evolving loci contribute to species divergence by accumulating changes themselves and by affecting interacting loci, which in turn evolve rapidly[1,2,3]
Like HP1A, which is shown to localize exclusively to heterochromatin, HP1D and HP1E localize to centromeric heterochromatin, HP1D is predominantly expressed in the ovaries, while HP1E is predominantly expressed in the testes
To test for evidence of positive selection, we first analyzed single sequences of D. melanogaster, D. simulans, D. sechellia, D. yakuba and D. erecta for the 11 genes associated with Condensin I formation and centromere localization (Table 1)
Summary
Evolving loci contribute to species divergence by accumulating changes themselves and by affecting interacting loci, which in turn evolve rapidly[1,2,3]. Fast evolution has been shown in centromeric sequences, which are comprised of rapidly evolving, tandemly repeated satellite DNAs13 Evolution of these repeats can drive changes in centromere-associated proteins, often resulting in coevolution through positive selection at interacting partners[1,14]. HP1s are known to be important in chromosome assembly and stability[29,30,31], and have been shown to play a role in cohesion recruitment to pericentric heterochromatin in yeast[32] This process may result in more rigid centromeric regions which enable the chromosome to withstand the forces associated with spindle attachment, and subsequent chromosome separation[29,31] without which, aberrant segregation of chromosomes could be more abundant.
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