Retention of a single Cenp-C gene in different syntenic locations in the montium group of Drosophila species
Chromosome segregation in eukaryotes requires the orchestrated interaction of chromosomes with microtubules, mediated by the kinetochore multiprotein complex that assembles on specific chromosomal regions known as centromeres. In most eukaryotes, two centromeric proteins, CenH3 and Cenp-C, are essential for centromere function. In Drosophila, the localization of CenH3 (referred to as Cid in Drosophila) depends on its chaperone CAL1 and Cenp-C. Previous studies have shown that both Cid and Cenp-C underwent a coincident gene duplication and likely functional specialization in the Drosophila subgenus. Independently, Cid duplications led to Cid1, Cid3, and Cid4 paralogs in the montium group (Sophophora subgenus), but it is unknown whether this group also underwent parallel duplications of Cenp-C. Here, we investigate this possibility by analyzing sequenced genomes of 23 montium group species. We identified Cenp-C genes in five distinct syntenic loci; we named these genes Cenp-C1b, Cenp-C1c, Cenp-C1d, Cenp-C1e and Cenp-C3. Despite their distinct synteny, most montium group species only encode a single Cenp-C; their phylogeny mirrors the species phylogeny, and they appear to have retained Cenp-C protein motifs indicative of function. A closer examination revealed that these Cenp-C genes resulted from gene translocations or alternate retention (duplication followed by loss of the ancestral copy); only one species, D. vulcana, retains two intact Cenp-C paralogs. Therefore, unlike the Drosophila genus, the co-retention of three Cid paralogs in the montium group has not resulted in a coincident Cenp-C paralog co-retention. Our work highlights differences in functional retention and likely specialization of the two most conserved centromeric proteins in eukaryotes.