engleski

Organizational pattern of satellite arrays indicate high dynamics of recombinational events in centromeric heterochromatin of tenebrionid beetles

It has been shown that long homogeneous domains of satellite repeats, occasionally interrupted with transposable elements are principal DNA sequences involved in centromeric function and heterochromatin formation of animal and plant species, such as human, Drosophila and rice. Large blocks of centromeric heterochromatin of tenebrionid beetles (Insecta, Coleoptera) are composed of several satellite DNAs. Irrespectively to significant differences in copy number, all satellites colocalize in centromeric heterochromatin of all chromosomes. Monomers of each satellite form irregular patchwork of short, not longer than 100 kb, homogeneous arrays mutually interspersed within domains of several Mb in length. Interspersion pattern lacks any specificity, which would distinguish between pericentromeric and centromeric heterochromatin, or indicate position of functional centromere. In Tribolium madens, junctions between arrays of two satellites are sites of abrupt transition from one satellite to the other. At some junctions monomer sequences of adjacent satellites do not differ from the others in the repetitive family. Alternatively, highly divergent monomers located at the junctions are gradually replaced with less and less divergent variants towards the interior of the satellite array. This distribution of variants is consistent with unequal crossing over as a mechanism of homogenization of satellite arrays. Physical basis for high level of exchange events could be in a bouquet stage of meiotic prophase I, in which all chromosomes are tightly aligned with their centromeric heterochromatin in a globular structure. In contrast to the established opinion, organizational structure of centromeric heterochromatin in tenebrionid beetles indicates that heterochromatin formation and centromeric function are not necessarily incompatible with high dynamics of recombination events.

repetitive DNA; centromeric heterochromatin; satellite arrays; unequal crossover; Coleoptera

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