The chromosomes of longnose gar, Lepisosteus osseus, an extant representative of early radiation of actinopterygian fishes, were studied using conventional Giemsa-staining, Ag-staining, CMA3-fluorescence and fluorescence in-situ hybridization (FISH). The diploid chromosome number was 2n = 56 and the karyotype contained 11 pairs of metacentric, 6 pairs of submetacentric, 3 pairs of subtelocentric macrochromosomes and 16 microchromosomes. Nearly all macrochromosomes showed large CMA3-positive regions resembling the R-bands of higher vertebrates, indicating extensive distribution of GC-rich DNA along chromosomes. The nucleolar organizer regions (NORs) were located on the end of the short arm of a single small metacentric macrochromosomal pair. These sites were strongly CMA3-positive, suggesting that ribosomal sites are associated with GC-rich DNA. In-situ hybridization (FISH) with a rDNA probe gave consistently positive signals in the same regions detected by Ag-staining and CMA3-fluorescence. The evolutionary conservation of positive CMA3-fluorescence of ribosomal sites in 'holostean' and teleostean fishes is discussed.
Bibliographical noteFunding Information:
This study was supported by grants from the Grant Agency of Academy of Sciences of CR A6045704 (P.R. and M.R.), US National Academy of Sciences (P.R. and R.B.P.), the NRI Competitive Grants Program/USDA (93-37205-9171) (K.M.R.). We greatly appreciate the technical assistance of Miss Jana BucÏková. A. Suzuki, Tokyo University of Agriculture, Hokkaido, kindly provided and translated the Japanese papre by Ueno (1985).
- Chromomycin A-banding
- Fish cytogenetics
- GC-rich heterochromatin
- Longnose gar