Cytogenetics in Arctica islandica (Bivalvia, Arctidae): the Longest Lived Non-Colonial Metazoan

Abstract

Due to its extraordinary longevity and wide distribution, the ocean quahog Arctica islandica has become an important species model in both aging and environmental change research. Notwithstanding that, most genetic studies on ocean quahogs have been focused on fishery related, phylogeographic and phylogenetic aspects but nothing is known about their chromosomes. In this work, the chromosomes of the ocean quahog Arctica islandica were analysed by means of 4′,6-diamidino-2-phenylindole (DAPI)/propidium iodide (PI) staining and fluorescent in situ hybridization (FISH) with rDNA, histone gene and telomeric probes. Whilst both 5S rDNA and 45S rDNA were clustered at single subcentromeric locations on the long arms of chromosome pairs 2 and 12, respectively, histone gene clusters located on the short arms of chromosome pairs 7, 10 and 17. As happens with most bivalves, the location of the vertebrate type telomeric sequence clusters was restricted to chromosome ends. The knowledge of the karyotype can facilitate the anchoring of genomic sequences to specific chromosome pairs in this species.

Sequence Composition Underlying Centromeric and Heterochromatic Genome Compartments of the Pacific Oyster Crassostrea gigas

“…rDNA sequence derivatives can be also found as tandem repeats showing homology to intergenic sequences [ 51 , 52 , 53 , 54 ]. Chromosomal mapping revealed the centromere-proximal location for some of rDNA clusters in different bivalve species [ 55 , 56 , 57 , 58 , 59 ], as well as in other organisms, such as in the plant Arabidopsis thaliana [ 60 ]. In addition, Robicheau et al [ 61 ] report rDNA sequences appearing at multiple sites on chromosomes without forming rDNA arrays, presence of centromere-associated rDNA hits, and divergence of these sequences to pseudogenes.…”

Karyotype Characterization of Nine Periwinkle Species (Gastropoda, Littorinidae)

“…In contrast, the chromosomal location of the cluster varied from species to species: subcentromeric signals appeared in rough and flat periwinkles, intercalary ones in common and small periwinkles, and subterminal ones in mangrove and beaded periwinkles. The presence of these clusters at subterminal positions is quite unusual in invertebrate species and has only been described in some grasshoppers [ 39 ] and bivalves [ 25 , 28 , 40 , 41 , 42 , 43 ].…”

“…The morphological identification of the specimens was confirmed by amplifying and sequencing a fragment of the mitochondrial cytochrome c oxidase subunit I ( COI ) gene [ 27 , 28 ]. All sequences were deposited in the NCBI GenBank database under the accession numbers MH809396 to MH809424 ( Supplementary materials Figure S1 ).…”