engleski

Evolution of satellite DNAs from the genus Palorus : experimental evidence for the library hypothesis

Satellite DNA profiles have been characterized in the congeneric species Palorus ratzeburgii, P. subdepressus, P. genalis and P. ficicola (Coleoptera, Insecta). Each of them contains a single, A+T rich, major satellite DNA comprising a considerable portion of the genome. The major satellites exhibit insignificant mutual sequence similarity. Using PCR assay it has been shown that all four sequences are present in each of the tested Palorus species: one of them amplified into a high copy number major satellite, while the three others are in the form of low copy number repeats estimated to make approximately 0.05% of the genome. Each of the four satellites is interspecifically highly conserved concerning the sequence, monomer length and tandem repeat organization. Major, as well as low-copy-number satellites are colocalized in the regions of pericentromeric heterochromatin on all chromosomes of the complement. The low-copy-number satellites are dispersed between the large arrays of the major satellite over the whole heterochromatic block. Our results explain satellite DNA evolution confirming the hypothesis that related species share a "library" of conserved satellite sequences some of which could be amplified into a major satellite. Due to the evolutionary dynamics of satellite DNAs the content of the "library" is variable, the elimination of some sequences parallels the creation of the new ones. Quantitative changes in satellite DNAs, induced by occasional amplification of satellite repeat from the "library", could possibly occur in the course of speciation process, thus forming species specific profile of satellite DNAs.

Palorus; Coleoptera; satellite DNA; repetitive DNA; evolution; heterochromatin

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