Molecular Biological Characterization Of Oyster Chromosomes

In this study the traditional banding technique and fluorescence in situ hybridization (FISH) technique were used to characterize and identif the chromosomes of oysters. We developed chromosome-specific FISH probes by mapping a variety of repetitive DNA and P1 clone DNAs by FISH. The Pacific oyster trisomy 10 was successfully identified using chromosome-specific probes. The results of this study are listed as followings: I .The (3 and C banding distribution were analyzed in the eastern oyster chromosomes. Each chromosome has its unique banding characteristics. Differences in banding characteristics among some chromosomes (such as Chromosome 1 and 4, Chromosome 7 and 9) were not outstanding. G banding is susceptible to interference by variations such as the state of chromosome contraction. C banding pattern is highly reproducible and clear, C banding mainly distributed at the centromere and telomere region. Although C and 0 banding identified all chromosomes of the eastern oyster after intensive screening and careful analysis, they were not suitable for routine identification of oyster chromosomes. 2. Metaphase chromosomes prepared from early embryos and trocorphore stage were adequate for use in FISH analysis. The methods of chromosome preparing are highly producible and easily applied to other marine mollusc species. 3. Chromosomal localization of multiple gene DNA were performed by FISH. 1) 1 8S-5.8S rDNA was assigned to one locus in 5 Crassostrea oyster species studied, in the Pacific species (C.gigas, C. ariakensis and C. plicatula) , rDNA was localized to the telomeric region of the long arm of Chromosome 10; And in the Atlantic species (C. virginica and C. rhizophorae), rDNA was localized to the telomerie region of the short arm of Chromosome 2. .2) 1 8S-28S rDNA was assigned to two loci in 2 clam species studied. rDNA was assigned to the telomezic region of Chromosome 15 and Chromosome 19 in dwarf-surf clani (Mulinis Lateralis Say), and the same sequence was assigned on the proximal region of long arm of Chromosome 10 and on the telomere of short arm of Chromosome 12 in the hard clam (Me rcenaria mercenaria Linnaeus). The signal intensity was variable between two pairs of chromosomes. 3) 55 rDNA was assigned to the interstitial region inirnediately next to the centromere on the short arm of Chromosome 5 and the interstitial region of the short arm of Chromosome 6 in the eastern oyster. The signal intensity was not significantly variable between two pairs of chromosomes. 5S rDNA can serve as a specific marker for the identification of two pairs of homologous chromosomes in the eastern oyster. 4 Chromosome localization of some repetitive sequences were studied. 1) Two short repetitive sequences 1 P2 and I G8 produced strong hybridization signals dispersed on every chromosome in the eastern oyster. The signals were dispersed through all the chromosomes under low stringency, although the signals intensity was much lower under high stringency, the signals were still on every chromosome, suggesting this two sequences are dispersed in the oyster genome. 2) A satellite repetitive sequence Cgl 70 was mapped to centromeric regions of seven pairs of the Pacific oyster chromosomes. No interstitial site was found. FISH signals were strong and consistent on Chromosomes I, 2, 4 and 10, but weak or variable on Chromosomes 5, 8 and 10. No signals were observed on Chromosomes 3, 6 and...