title: Chromosomal characteristics of ribosomal DNA in the primitive semionotiform fish, longnose gar Lepisosteus osseus.
abstract: 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.
authors.affiliation: Laboratory of Fish Genetics, Institute of Animal Physiology and Genetics, Czech Academy of Sciences, Libechov, Czech Republich. rab@iapg.cas.cz
authors.forename: P
authors.initials: P
authors.lastname: Ráb
authors.forename: M
authors.initials: M
authors.lastname: Rábová
authors.forename: K M
authors.initials: KM
authors.lastname: Reed
authors.forename: R B
authors.initials: RB
authors.lastname: Phillips
mesh_terms: D000818:Animals; D002871:Chromosome Banding; D002875:Chromosomes / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D005260:Female; D005399:Fishes / Q000235:genetics*; D006570:Heterochromatin; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008297:Male; D009697:Nucleolus Organizer Region; D011003:Ploidies; D016622:Silver Staining; D014922:Wisconsin
chemical_list: D004275:DNA, Ribosomal; D006570:Heterochromatin