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Characteristics and distribution of TCAST satellite DNA in Tribolium castaneum euchromatin and its possible role in gene expression

In the red flour beetle Tribolium castaneum the major TCAST satellite DNA accounts for 35% of the genome and encompasses the pericentromeric regions of all chromosomes. Due to the presence of transcriptional regulatory elements and transcriptional activity in these sequences, TCAST satellite DNAs have also been proposed to be modulators of gene expression within euchromatin. Here is analyzed the distribution of TCAST homologous repeats in T. castaneum euchromatin, and studied their association with genes as well as their potential gene regulatory role. There are identified 68 arrays composed of TCAST-like elements distributed on all chromosomes. Based on sequence characteristics the arrays were composed of two types of TCAST-like elements. The first type consists of TCAST satellite-like elements in the form of partial monomers or tandemly arranged monomers, up to tetramers, while the second type consists of TCAST-like elements embedded with a complex unit that resembles a DNA transposon. TCAST-like elements were also found in the 5' UTR of the CR1-3_TCa retrotransposon, and therefore retrotransposition may have contributed to their dispersion throughout the genome. No significant difference in the homogenization of dispersed TCAST-like elements was found either at the level of local arrays or chromosomes, nor among different chromosomes. Of 68 TCAST-like elements, 29 were located within introns with the remaining elements flanked by genes within a 262 to 404 270 nt range. TCAST-like elements are statistically overrepresented near genes with immunoglobulin-like domains attesting to their non-random distribution and a possible gene regulatory role.

satellite DNA; repetitive DNA; gene regulation; transposone; Tribolium castaneum

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