Estudos citogenômicos em aves com foco na diferenciação do sistema cromossômico sexual ZZ/ZW

Abstract

One of the peculiarities of birds is the presence of a stable system of ZZ/ZW sex chromosomes, which originated in an ancestor approximately 70 million years ago. The group is also known for exhibiting karyotypes that present a relatively high level of conservation in relation to the diploid number (2n), generally close to 80 chromosomes, characterized by 10 pairs of macrochromosomes and 30 pairs of microchromosomes. The W chromosome of birds is characterized by frequently presenting an accumulation of repetitive sequences, such as satellite DNA, microsatellites and transposable elements, resulting from the processes of recombination suppression, which cause their morphological differentiation and the accumulation of these elements over time. Satellite DNAs (satDNAs), in turn, have been isolated and analyzed in several lineages, increasingly evidencing their contribution to the evolution of the karyotype and sex chromosomes, with the set of all satDNAs of a species being called Satelitoma. In this context, this work aimed to combine cytogenetic, genomic and bioinformatics analyses in the study of the evolution and differentiation of sex chromosomes in birds. For this purpose, we selected two study models (named A and B). In model A, we selected two species of the Turdidae family (named Turdus leucomelas and Turdus rufiventris), both with conserved 2n, 80 and 78, respectively. The isolation of the T. leucomelas satellitome was then performed, followed by fluorescence in situ hybridization (FISH) experiments in both species with the aim of identifying the conservation and divergence between the species, as well as their role in the differentiation of sex chromosomes. Additionally, we performed C-banding and comparative genomic hybridization (CGH) studies, in which we identified an atypical configuration of the ZZ/ZW sexual system in T. leucomelas, evidencing an alternative pathway for the evolution of the W chromosome. In model B, we selected two representatives of the Cariamidae family (Cariama cristata and Chunga burmeisteri), which present unusual karyotypes, with 108 and 106 chromosomes, respectively, with the Z chromosome being the largest component of both karyotypes. We compared FISH mapping of the satellites in C. cristata and corresponding in silico analyses. In addition, we compared the two isolated Satellitomes and analyzed the proportion of repetitive elements present in the Z chromosome, aiming to understand how these elements, combined with chromosomal rearrangements, may be associated with their growth in size. The findings provided a deeper understanding of the evolution of sex chromosomes in birds, demonstrating that the evolution of the Z and W chromosomes is considerably more complex than previously thought, encompassing chromosomal rearrangements and genomic alterations that diverge from the ancestral pattern.