Squamate reptiles show very dynamic genome structure between lineages (macro- and microchromosomes and no microchromosome in the genome) which might be associated with their richness at around 8,000 species. One genomic region that is an indicator of the dynamic state comprises satellite DNAs (stDNAs). These are highly repeated sequences constituting large portions of the heterochromatic region of any genome. At least four stDNA subfamilies coexist in varanid genomes and mostly differ in nucleotide sequences and copy number. Comparing stDNA subfamilies and species revealed that similarities between each sequence unit within different species of the same stDNA subfamily were higher than those of other stDNA subfamilies belonging to the same species. This suggests that stDNA families lack homogenized species-specific nucleotide positions in varanid lineages. These results agreed with the library model of stDNA evolution, in which diverse stDNA families or subfamilies coexist in the genomes of related species, with disparate amplification among species. By contrast, monomers of a stDNA family exhibit higher sequence similarity than the same stDNA family of related species in snakes, suggesting that mutations in stDNA monomers are homogenized and concomitantly fixed at species level. Additionally, stDNA sequences in snakes show no genomic compartmentalization between micro- and microchromosomes as a consequence of homogenized chromosome size-correlation. Conversely, stDNA sequences are specifically located on macrochromosomes in varanids, suggesting chromosome size-correlated compartmentalization between macro- and microchromosomes. Evolutionary dynamics of stDNA (e.g. copy number, nucleotide sequence, location) can, therefore, provide insights into genome organization and evolution
Squamate reptiles show very dynamic genome structure between lineages (macro- and microchromosomes and no microchromosome in the genome) which might be associated with their richness at around 8,000 species. One genomic region that is an indicator of the dynamic state comprises satellite DNAs (stDNAs). These are highly repeated sequences constituting large portions of the heterochromatic region of any genome. At least four stDNA subfamilies coexist in varanid genomes and mostly differ in nucleotide sequences and copy number. Comparing stDNA subfamilies and species revealed that similarities between each sequence unit within different species of the same stDNA subfamily were higher than those of other stDNA subfamilies belonging to the same species. This suggests that stDNA families lack homogenized species-specific nucleotide positions in varanid lineages. These results agreed with the library model of stDNA evolution, in which diverse stDNA families or subfamilies coexist in the genomes of related species, with disparate amplification among species. By contrast, monomers of a stDNA family exhibit higher sequence similarity than the same stDNA family of related species in snakes, suggesting that mutations in stDNA monomers are homogenized and concomitantly fixed at species level. Additionally, stDNA sequences in snakes show no genomic compartmentalization between micro- and microchromosomes as a consequence of homogenized chromosome size-correlation. Conversely, stDNA sequences are specifically located on macrochromosomes in varanids, suggesting chromosome size-correlated compartmentalization between macro- and microchromosomes. Evolutionary dynamics of stDNA (e.g. copy number, nucleotide sequence, location) can, therefore, provide insights into genome organization a ...
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