engleski

Organizational pattern of beetle satellite DNAs indicates high dynamics of recombinational events in centromeric heterochromatin

Heterochromatic chromosomal domains are the least understood genomic regions, highly underrepresented in outputs of sequencing projects due to repetitive nature of their DNA. Principal DNA components in heterochromatin are long arrays of tandemly repeated sequences, often called satellite DNAs. Recent data favor significance of satellite DNAs in centromeric function, and as sequences involved in formation of heterochromatic state through RNAi mechanism. Despite numerous data on satellite DNAs, little is known about sequential arrangement of satellite arrays, transition zones between them, and about the origin of diverse satellite (sub)families. Two related satellite families colocalize in centromeric heterochromatin of the tenebrionid beetle Tribolium madens. They form an irregular patchwork of short, up to 70 kb long, homogeneous arrays located within domains several Mb in length. Cloned hybrid genomic fragments revealed directly linked satellite families. While some adjacent monomers could not be distinguished from those cloned at random, some showed enhanced sequence divergence typical for repeats evolving at array ends, in zones of low homogenization efficiency. Multiple copies of the latter junction type support the hypothesis that sites of evolutionary origin of novel satellite (sub)families can be localized at array ends. Related satellites detected in the sibling species T. audax could be nascent by similar processes in an ancestral repetitive sequence. Observed patterns point to extensive recombinational processes in centromeric heterochromatin, resulting in a dynamic structure that changes dramatically over a short time frame.

repetitive DNA ; unequal crossing-over ; centromeric heterochromatin ; Coleoptera

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