Abstract
The subfamily Triatominae, vectors of Chagas disease, comprises 140 species characterized by a highly homogeneous chromosome number. We analyzed the chromosomal distribution and evolution of repeated sequences in Triatominae genomes by Genomic in situ Hybridization using Triatoma delpontei and Triatoma infestans genomic DNAs as probes. Hybridizations were performed on their own chromosomes and on nine species included in six genera from the two main tribes: Triatomini and Rhodniini. Genomic probes clearly generate two different hybridization patterns, dispersed or accumulated in specific regions or chromosomes. The three used probes generate the same hybridization pattern in each species. However, these patterns are species-specific. In closely related species, the probes strongly hybridized in the autosomal heterochromatic regions, resembling C-banding and DAPI patterns. However, in more distant species these co-localizations are not observed. The heterochromatic Y chromosome is constituted by highly repeated sequences, which is conserved among 10 species of Triatomini tribe suggesting be an ancestral character for this group. However, the Y chromosome in Rhodniini tribe is markedly different, supporting the early evolutionary dichotomy between both tribes. In some species, sex chromosomes and autosomes shared repeated sequences, suggesting meiotic chromatin exchanges among these heterologous chromosomes. Our GISH analyses enabled us to acquire not only reliable information about autosomal repeated sequences distribution but also an insight into sex chromosome evolution in Triatominae. Furthermore, the differentiation obtained by GISH might be a valuable marker to establish phylogenetic relationships and to test the controversial origin of the Triatominae subfamily.
Highlights
The repetitive DNAs distribution along chromosomes is one of the essential elements in evolutionary genetics for understanding the organization and the evolution of genomes [1]
Chromosome preparations for Genomic in situ hybridization (GISH) analyses were obtained from males of 11 triatomine species, included in the two principal tribes of the subfamily: Rhodniini and Triatomini (Table 1), which involve almost 90% of the 140 recognized species [17]
Our GISH results reveal the occurrence of two chromosomal hybridization configurations: a) very intense hybridization signals concentrated on specific chromosomal regions or particular chromosomes and b) lower intensity hybridization signals dispersed along all chromosomes (Figures 1, 2 and 3)
Summary
The repetitive DNAs distribution along chromosomes is one of the essential elements in evolutionary genetics for understanding the organization and the evolution of genomes [1]. Analyses of these sequences are even more important in organisms with holocentric chromosomes, such as hemipteran insects, where the lack of primary constriction, small chromosome size and the limited banding procedures makes chromosomal studies harder to achieve. The number of autosomes is remarkably constant; all species except 3 present 20 autosomes They have three sex systems in males (XY, X1X2Y and X1X2X3Y), being the sex chromosomes achiasmatic and showing a particular segregation called inverted meiosis or post-reduccional segregation [4]
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