Karyological analysis and FISH physical mapping of 18S rDNA genes, (GATA)n centromeric and (TTAGGG)n telomeric sequences in Conus magus Linnaeus, 1758

Abstract

Karyological analysis of gill tissue from the marine gastropod Conus magus showed a diploid chromosome number of 32. Three major groups of chromosomes were identified: 22 median region, 4 submedian region and 6 subterminal region chromosomes. The haploid count was verified using chromosomal spreads from ovarian cells. Fluorescence in situ hybridization (FISH) physical mapping of an 18S rDNA sequence showed a wide distribution of major, medium and minor hybridization sites. These hybridization sites were detected in two to four different regions—paracentromeric, centromeric, interstitial or telomeric—per chromosome. Identical 18S rDNA FISH signals were found in the putative pairs of homologous chromosomes. FISH profiles of tandem simple-sequence repeats (SSRs) were physically mapped in locations near centromeres (GATA)n or telomeres (TTAGGG)n, as well as in noncentromeric (GATA)n regions and nontelomeric (TTAGGG)n interstitial regions of whole chromosome arms. Similar SSR chromosome organization FISH patterns were observed in two chromosomal spreads from the same individual: (1) telomeric (TTAGGG)n sequences in both p and q terminals of 15 chromosomes (10 median region, 2 submedian region and 3 subterminal region) and (2) centromeric (GATA)n sequences in 23 chromosomes (13 median region, 4 submedian region and 6 subterminal region). The C. magus DAPI karyotype and genomic landmarks based on the FISH profiles of 18S rDNA, (TTAGGG)n and (GATA)n sequences may contribute to the elucidation of the evolution of the karyotypes of Conus species and in the detection and localization of Conus chromosomal genes using FISH.