Molecular and cytogenetic characterization of Crassostrea angulata chromosomes

We have conducted a molecular cytogenetic study of Crassostrea angulata, by treating its mitotic chromosomes with C-banding, fluorochrome and oligopeptide staining, restriction enzyme banding and fluorescent in situ hybridization, using three repetitive or multicopy DNAs (the GATA sequence, the TTAGGG telomeric repeat and the 5S rDNA). Results on C-banding indicate the presence of heterochromatin in several chromosomes occupying telomeric positions. The staining with DAPI, DA/DAPI and AMD/DAPI allow concluding that large regions rich in AT in the chromosomes of C. angulata do not exist. Restriction banding has shown few restriction sites for AluI (AGTC site) and a relative abundance of G-C in terminal and interstitial chromosome regions, inferred by the digestion with HaeIII (GGCC site) and BamHI (GGATCC site). In situ hybridization with GATA indicated that these repeated sequences are widely dispersed in the genome of this species, whereas hybridization with the telomeric repeat revealed small bright hybridization signals, uniform in size and intensity, on each telomere of all chromosomes but not in interstitial positions. Location of 5S rDNA displayed the presence of two 5S-bearing chromosome pairs, of large size, on the subterminal position of the karyotype of C. angulata, this location being different from the ones encoding the major ribosomal genes in chromosome pair 10 (described in a previous paper).