Histone H3 gene in the Pacific oyster, Crassostrea gigas Thunberg, 1793: molecular and cytogenetic characterisations

Abstract

Abstract. The Pacifi c oyster, Crassostrea gigas Thunberg, 1793 (2n = 20) is an economically important mollusc species cultured throughout the world. The most frequently used technique for molecular cytogenetic studies is fl uorescence in situ hybridisation which offers new opportunities for the identifi cation of oyster chromosomes. In oysters, it has been used to locate telomeric sequences, satellite DNA, simple sequence repeats, ribosomal RNA genes, and bacteriophage P1 clones. However, regarding chromosome identifi cation, no study has been done with histone H3 gene. Histone H3 is among the most conserved eukaryotic proteins. Most histone H3 genes are repeatedly organised into clusters, which make them an ideal chromosomal marker. In bivalves, some data exist concerning sequence information but little knowledge is available concerning the physical mapping of histone genes. The histone H3 gene was sequenced in C. gigas and phylogenetic analysis revealed that C. gigas was more closely related to Ostrea edulis Linnaeus, 1758 and species of the genus Mytilus Linnaeus, 1758. In C. gigas, the histone H3 gene was mapped on two different pairs of chromosomes, one at an interstitial site on the long arm of chromosome pair 4, and the other on the telomeres of the smaller chromosome pair (pair 10). Polymorphism was detected on the telomeres of pair 10, once it was possible to observe single or double signals. Comparative chromosomal mapping should improve our understanding of bivalve genome organisation.

A preliminary integrated genetic map distinguishes every chromosome pair and locates essential genes related to abiotic adaptation of Crassostrea angulata/gigas

“…However, after using standard FISH protocols that are usually applied to multigene families [ 28 ], a second signal was detected in a medium-size chromosome. In C. gigas the location of the H3 gene has been described [ 42 ], but the position described is not consistent with our findings, since those authors described two hybridization signals on chromosome pairs 4 and 10. It could be argued that the position 3 observed in our results is different from chromosome pair 4, owing to an absence of chromosomal markers in that work leading to a mistake being made between the two chromosome pairs (3 and 4) that are almost identical in size and morphology.…”

“…It could be argued that the position 3 observed in our results is different from chromosome pair 4, owing to an absence of chromosomal markers in that work leading to a mistake being made between the two chromosome pairs (3 and 4) that are almost identical in size and morphology. Our results show that the position is not in chromosome 4 as described by Boully et al [ 42 ], because that position is occupied by 5S rDNA genes [ 28 , 45 ]. However an even more relevant result is that histone genes are not in chromosome 10 [ 42 ], because that is the chromosome that bears major ribosomal genes described in the Pacific and Portuguese oysters [ 15 , 46 ], and the double FISH carried out in this study confirms that the two families are not co-localized.…”

“…Our results show that the position is not in chromosome 4 as described by Boully et al [ 42 ], because that position is occupied by 5S rDNA genes [ 28 , 45 ]. However an even more relevant result is that histone genes are not in chromosome 10 [ 42 ], because that is the chromosome that bears major ribosomal genes described in the Pacific and Portuguese oysters [ 15 , 46 ], and the double FISH carried out in this study confirms that the two families are not co-localized. For that reason, the location of the histone genes should be revised because contradictory results have been obtained in those experiments.…”

“…In order to label 5S rDNA and 18S rDNA multigene families, PCR amplifications with biotin-16-dUTP or digoxigenin-11-dUTP (Roche Molecular Biochemicals) were made [ 28 ]. For the H3 histone gene the primers H3F (5’-CGTAAATCCACTGGAGGCAAGG-3′) and H3R (5’-GGATGGCGCACAGGTTGGTGTC-3′) were used [ 42 ]. The H4 histone genes were amplified by primers H4-F (5’-TGAGAGATAACATCCAGGGTATCAC-3’) and H4-R (5′- CTCTTGAGGGCGTAGACAACGTCCAT-3′).…”

Divergent evolutionary behavior of H3 histone gene and rDNA clusters in venerid clams

“…Usually, the clusters comprise only core histone genes but repeated clusters including linker histone and/or other genes have also been reported. In these organisms histone H3 genes have been mapped to chromosomes in only eight mussels [ 13 , 14 , 17 – 20 ], four scallops [ 21 ], one oyster [ 22 ] and two clams [ 23 ]. In comparison with 45S and 5S rDNA clusters, surprisingly remarkable differences in number and location of the histone H3 gene clusters were found, more outstandingly among mussels and clams.…”