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Identification, characterization and localization of satellite DNA sequences of the Pacific oyster Crassostrea gigas (Thunberg, 1793)

Bivalve mollusks are a large group of economically and ecologically important invertebrates, which made them particularly interesting as model organisms for genomic research. So far, 31 bivalve genomes have been sequenced, the first one being the genome of the Pacific oyster Crassostrea gigas (Thunberg, 1793), now assembled to the level of chromosomes. Repetitive DNA sequences constitute the largest part of the most eukaryotic genomes. Satellite DNAs (satDNAs) are the most numerous and usually build very long arrays of tandemly repeated monomers preferentially located in the heterochromatin [1]. Although they are involved in important functions regarding the stability of chromatin, due to their repetitive nature and almost identical monomers they are very often underrepresented in the genome assemblies making them still quite unexplored. Low content of heterochromatin [2] and the association of satDNAs with transposable elements[3], make the genome of the Pacific oyster an interesting research topic. In order to identify a complete set of satDNAs (satellitome) of the Pacific oyster, we isolated genomic DNA and sequenced it using next-generation sequencing platform. The obtained reads were analyzed using TAREAN (Tandem Repeat Analyzer) pipeline yielding a set of 52 satDNAs. All satDNAs were compared to an online base of repetitive sequences, Repbase. More than 50% of satDNAs showed similarity to DNA transposons, half of which were Helitrons. The whole set of identified satDNAs was localized in silico on publicly available chromosomes of the Pacific oyster, and several were localized on metaphase chromosomes using fluorescence in situ hybridization. Chromosomal distribution exhibiting mostly interspersed pattern is related to the association of satDNAs with mobile elements. In this work, we identified and characterized the satellitome of the Pacific oyster and localized several satDNAs of interest, furthering our knowledge about the unexplored genome components of the Pacific oyster.

školjkaši, Crassostrea gigas, satelitne DNA, Helitroni

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