Abstract
Choloepus, the only extant genus of the Megalonychidae family, is composed of two living species of two-toed sloths: Choloepus didactylus and C. hoffmanni. In this work, we identified and characterized the main satellite DNAs (satDNAs) in the sequenced genomes of these two species. SATCHO1, the most abundant satDNA in both species, is composed of 117 bp tandem repeat sequences. The second most abundant satDNA, SATCHO2, is composed of ~ 2292 bp tandem repeats. Fluorescence in situ hybridization in C. hoffmanni revealed that both satDNAs are located in the centromeric regions of all chromosomes, except the X. In fact, these satDNAs present some centromeric characteristics in their sequences, such as dyad symmetries predicted to form secondary structures. PCR experiments indicated the presence of SATCHO1 sequences in two other Xenarthra species: the tree-toed sloth Bradypus variegatus and the anteater Myrmecophaga tridactyla. Nevertheless, SATCHO1 is present as large tandem arrays only in Choloepus species, thus likely representing a satDNA exclusively in this genus. Our results reveal interesting features of the satDNA landscape in Choloepus species with the potential to aid future phylogenetic studies in Xenarthra and mammalian genomes in general.
Highlights
A significant part of eukaryotic genomes, ~ 30% in some plants to more than 50% in some insects and mammals, is composed of tandemly organized highly repetitive sequences, known as satellite DNAs
The analysis indicated differences in the proportion of satellite DNAs (satDNAs) in the two species: the satDNA content represents > 13% of the C. didactylus genome, whereas this value is approximately 3% in C. hoffmanni
The SATCHO2 sequence did not amplify by polymerase chain reaction (PCR) with the genomic DNAs of neither B. variegatus nor M. tridactyla (Supplementary Fig. 2). These results suggest that, SATCHO1 and SATCHO2 are present outside the genus Choloepus, these sequences are not distributed as abundant long arrays of tandem repeats in other Xenarthra genera, in which they should not be classified as satDNAs
Summary
A significant part of eukaryotic genomes, ~ 30% in some plants to more than 50% in some insects and mammals, is composed of tandemly organized highly repetitive sequences, known as satellite DNAs (satDNAs) (reviewed in Ref.[1]). SatDNAs are major components of the constitutive heterochromatin present in fundamental chromosome structures, such as centromeres and telomeres (reviewed in Refs.[1,2]) They have been shown to be important components of chromosome organization, pairing, and segregation. Short dyad symmetry sequences have been identified in satellite DNA-free centromeres and in centromeric satDNAs which lack CENP-B boxes[7]. SatDNAs are important components in the evolution of eukaryotic genomes They can evolve three times faster than intergenic regions, which often results in significant differences between sequences, even among closely related species (reviewed in Ref.[1]). Because new mutations are constantly spread by molecular drive, intraspecific satDNA arrays are often composed of very similar tandemly repeated sequences that have the potential to be used as species-specific markers
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