Restriction enzyme digestion chromosome banding in Crassostrea and Ostrea species: comparative karyological analysis within Ostreidae

Reliable banding techniques are a major necessity for genetic research in oysters. In this study, we carried out the cytogenetic characterization of four oyster species (family Ostreidae) using restriction endonuclease treatments. Chromosomes were treated with three different restriction enzymes, stained with Giemsa, and examined for banding patterns. The following species were studied: Crassostrea gigas (2n = 20; total number of bands with ApaI, 74; HaeIII, 61; PstI, 76), Crassostrea angulata (2n = 20; ApaI, 62; HaeIII, 61; PstI, 55) (subfamily Crassostreinae), Ostrea edulis (2n = 20; ApaI, 82; HaeIII, 59; PstI, 66), and Ostrea conchaphila (2n = 20; ApaI, 68; HaeIII, 62; PstI, 69) (subfamily Ostreinae). Treatment of samples with ApaI, HaeIII, and PstI produced specific banding patterns, which demonstrates the potential of these enzymes for chromosome banding in oysters. This is of special interest, since it has been recently shown in mammalian chromosomes that restriction enzyme banding is compatible with fluorescence in situ hybridization. This study therefore provides a fundamental step in genome mapping of oysters, since chromosome banding with restriction enzymes facilitates physical gene mapping in these important aquaculture species. The analysis of the banded karyotypes revealed a greater similarity within the genera of Crassostrea and Ostrea than between them.Key words: Ostreidae, Crassostrea, Ostrea, chromosome banding, in situ restriction enzyme banding.

Cytogenetics of chromosome rearrangements in Tribolium castaneum

The karyotype of the red flour beetle, Tribolium castaneum, was reexamined and improved by restriction enzyme banding with HpaII. After this treatment, each of the 10 chromosomes were identified in spermatogonial metaphase cells and 3 of the 8 autosomal bivalents and the XY pair were identified in spermatocyte metaphase I nuclei. Based on centromere position, relative length, and banding pattern, probable correlations between some of the mitotic chromosomes and some of the metaphase I bivalents were ascertained. Thus improved, the karyotypes of beetles harboring genetically defined translocations were investigated. Spermatocyte metaphase I nuclei were most informative, as normal chromosome pairing was visibly disrupted by rearrangements. Bivalents associated with each rearrangement were identified. Results demonstrated that each of the five best defined T. castaneum linkage groups corresponds to a different chromosome and established correspondence between bivalents and linkage groups 1–4. The relevance of these findings is discussed with regard to Tribolium genetics and evolution.Key words: beetles, red flour beetle, Coleoptera, linkage groups, chromosome banding.