A centromeric satellite sequence in the Pacific oyster (Crassostrea gigas Thunberg) identified by fluorescence in situ hybridization

A highly repetitive satellite sequence was previously identified in the Pac ific oyster Crassostrea gigas Thunberg. The sequence has 168 bp per unit, p resent in tandem repeats, and accounts for 1% to 4% of the genome. We studi ed the chromosomal location of this satellite sequence by fluorescence in s itu hybridization (FISH), A probe was made by polymerase chain reaction and incorporation of digoxigenin-11-dUTP. Hybridization was detected with fluo rescein-labeled antidigoxigenin antibodies. FISH signals were located at ce ntromeric regions of 7 pairs of the Pacific oyster chromosomes. No intersti tial site was found. Signals were strong and consistent on chromosomes 1, 2 , 4, and 7, but weak or variable oil chromosomes 5, 8, and 10. No signal wa s observed on chromosomes 3, 6, and 9. Our results showed that this sequenc e is clearly a centromeric satellite, disputing its previous assignment to the telomeric and submetacentric regions of 2 chromosomes. No signal was de tected in the American oyster (Crassostrea virginica Gmelin).