Identificação e caracterização dos satelitomas de oito espécies de Xenarthra

Abstract

Satellite DNAs (satDNAs) are highly repetitive sequences that form long arrays and are the main components of constitutive heterochromatin. Their transcripts (ncRNA) are related to essential biological functions such as maintenance, organization, and correct functioning of the centromeric and telomeric regions. Despite their importance, satDNAs represent a poorly studied fraction of eutherian genomes. In this work we identified and characterized the most abundant satDNAs in the genomes of eight Xenarthra species using in silico and cytogenomic analyses. In Chapter 1, we identified two satDNAs in the genomes of the two-toed-sloths from the genus Choloepus, SATCHO1 (117bp) and SATCHO2 (2292bp). SATCHO1 was the most abundant satDNA in both species. Using fluorescence in situ hybridization (FISH) experiments, we mapped these two sequences onto C. hoffmanni chromosomes. The two sequences colocalized in the centromeric region of all chromosomes, except the X. SATCHO1 and SATCHO2 have some characteristics that suggest centromeric function, such as the presence of centromeric protein B binding sites (CENP-B box), pairs of small dimers and the formation of possible stable secondary structures. In Chapter 2, we used in silico tools to identify 39 satDNA sequences in the genomes of six Xenarthra species (Bradypus variegatus, Myrmecophaga tridactyla, Tamandua tetradactyla, Chaetophractus vellerosus, Dasypus novemcinctus, and Tolypeutes matacus). The in silico analyses allowed us to identify ten of these 39 satDNAs as belonging to the SATCHO1 family and one belonging to the SATCHO2 family. All satDNAs from the SATCHO 1 and 2 families have characteristics suggestive of centromeric functions, such as the presence of the CENP-B box, small pairs of palindromic sequences, and the formation of possible stable secondary structures. Furthermore, five satDNAs have higher-order arrangements, ranging from four to six 117bp internal repeats. In Chapter 3, we describe the cytogenomic characterization of six satDNAs present in the genomes of M. tridactyla and T. tetradactyla. SatDNA MTR156 was mapped by FISH to the terminal regions of almost all M. tridactyla autosomes and in some pairs of T. tetradactyla. Telomeric probes mapped to pericentromeric regions of six M. tridactyla autosomes, coinciding with constitutive heterochromatin regions revealed after CBG banding. This work presents for the first time more detailed analyses of repetitive DNA content of a considerable number of Xenarthra species, a phylogenetically basal group among eutherians, with an eminently South American distribution and evolutionary history that still poorly studied.