engleski

Contrasting patterns in genomic composition of satellite DNA repeats

Satellite DNAs (satDNAs) are principal DNA components that build heterochromatic chromosomal regions. However, extremely different concepts can characterize satDNA organization in particular organisms, mirroring heterochromatin abundance and distribution. Key feature of heterochromatin and satDNA organization in tenebrionid beetles is a highly abundant major satDNA (> 50% of genomic DNA) and a number of low-copy tandem repeats intermingling in (peri)centromeres of all chromosomes. The lack of chromosome specificity suggests that the whole pericentromeric heterochromatin in these species acts as a unique homogenization domain, regardless the satDNA family or its abundance. SatDNA composition in the bivalve mollusk Donax trunculus contrasts the above described concept, having less prominent heterochromatin regions distributed in telomeric and interstitial chromosomal locations, with no cytogenetically detectable heterochromatin located around centromeres. Nine satDNAs, that we characterized in this organism so far, are present in a low copy number, mostly composing less than 1 % of genomic DNA, with no evidence of highly abundant satDNA component comparable to that found in beetles. Although the distribution of constitutive heterochromatin is not uniform in all bivalve species, low amounts of heterochromatin and large number of poorly represented satellite (sub)families can be taken as a characteristic of this group of organisms. Differences in organizational patterns of satellite DNAs and heterochromatin may be explained as a consequence of organism-group specificities in homogenization mechanisms that in synergy with organizational and structural properties of satDNAs make a complex network of interactions resulting in the observed sequence distribution.

satellite DNA; heterochromatin; inerspersed repeats; beetles; molluscs

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