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Diversification of satellite DNA variants in Donax trunculus genome

Satellite DNAs are non-coding, tandemly repeated DNA sequences that comprise long arrays in the genome and are usually located within heterochromatic regions of chromosomes. Among marine invertebrates, satellite DNAs have so far been studied in only a couple of species including the mollusc Donax trunculus. In D. trunculus, five distinct satellite families have been described previously. They are all present in low number of copies and are distinct in their monomer sequence although some families share oligonucletide motifs. We have discovered two new satellites resident within D. trunculus genome. Even though they share the same monomer length, they are dissimilar in nucleotide sequence, AT content and genomic abundance. One of the satellites is characterized by extensive grouping of monomer sequence variants into subfamilies identified by distinctive combinations of diagnostic nucleotides. Furthermore, at least one subfamily was created through amplification of adjacent repeats in a higher order register. However, sequence analysis also revealed the persistence of conserved segments within the satellite monomer, which stands in contrast to the sequence and organizational differences that accumulated between subfamilies of monomer variants, and may indicate constraints in the evolution of satellite repeats.

molluscs; tandem repeats; sequence variants; evolutionary constraints

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