engleski

Two-stage model of evolution of satellite DNA sequences: an interplay of selective constraints and stochastic events

Satellite DNAs are tandemly arranged, highly repetitive sequences located in the constitutive heterochromatin of all eukaryotes. According to the library model, related species have in common satellite DNA sequences amplified in differing abundances: species-specificity of satellite profiles results primarily from rapid fluctuations in the monomer copy-number while nucleotide sequences of satellite DNAs can remain unchanged for significant evolutionary periods. Analysis of related satellites coexisting in the library of parthenogenetic root-knot nematodes disclosed three levels of variability along the monomer sequences that modulated accumulation of sequence divergences during formation of extant satellites. These observations indicate a possible paradox in the evolution of satellite sequences, since some satellites distributed in species separated over long-time periods do not show any specific traits even in polymorphic segments of their monomers. We propose a two-stage model in the evolution of at least some satellite sequences. In the first stage, the necessity to meet functional requirements might determine formation of diverged satellite variants, their spread and survival in the library. In the second stage, homogenization mechanisms acting on whole-length monomers of new satellites can favor persistence of established mutational profile along the entire monomer sequence (i.e. both in "conserved" and "variable" sequence segments). In the same time, stochastic events can be dominant in differential amplification of satellite DNAs of similar properties in the library.

satellite DNA; concerted evolution; library hypothesis; root-knot nematodes

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