Evolução do gene da proteína centromérica Cenp-C em espécies de Drosophila do grupo montium

Abstract

The centromere is the region necessary for chromosomal segregation in eukaryotes. In animals and plants, functional centromeres are initiated by the interaction between satellite DNAs and the Cenp-A protein, a variant of histone H3 (CenH3) unique to the centromeric chromatin. Another centromeric protein, Cenp-C, binds to Cenp-A and centromeric DNA (cenDNA), providing the basis for the recruitment of other kinetochore proteins. Given the functional importance of centromeres, high evolutionary conservation of their structure among species would be expected. However, both cenDNA and Cenp-A/Cenp-C evolve rapidly. According to the centromere drive hypothesis, this is due to the deleterious effects associated with cenDNA expansions, and positive selection at Cenp-A and Cenp-C sites that suppress these effects. In species of the subgenus Drosophila, duplications of the gene of Cid (CenH3 of Drosophila) (Cid1 or Cid6 and Cid5) and Cenp-C (Cenp-C1 and Cenp-C2) were found. According to differential expression patterns of these genes in different tissues, it was suggested that Cid1 interacts with Cenp-C1 and Cid5 with Cenp-C2 for centromeric function. In the montium group species (subgroup Sophophora), duplications of Cid (Cid1, Cid3, and Cid4) were observed and these paralogs also revealed differential expression depending on the tissue. This work had as main objectives to investigate (i) if there are duplications of Cenp-C in these species and (ii) to test if there is positive selection in Cenp-C. For this, we used recently sequenced genomes from 23 montium group species. We found three new copies of the Cenp-C gene, which we called Cenp-C3, Cenp-C4, and Cenp-C5. However, all species have only one copy of Cenp-C in the same genome, except for D. vulcana, which has two (Cenp-C1 and Cenp-C5). This result indicates that only one copy of Cenp-C should interact with the three Cid paralogs present in the montium group species. Our analyzes showed that the three new copies originated from independent duplications of Cenp-C1, with subsequent loss of Cenp-C1 in most species. We found positive selection signatures in four Cenp-C amino acids located in intermediate regions of Cenp-C. Although we do not know which regions of Cenp-C make direct contact with DNA, Cenp-C may be evolving under positive selection to suppress the centromeric drive. Taken together, our results help to understand the consequences of gene duplications for the structure and evolution of centromeres.