title: Analyses of the structure of NORs in two species of South American Sorubiminae fishes (Siluriformes) by means of several cytogenetic techniques.
abstract: Several cytogenetic techniques (AgNOR, C- G- and RE bandings, DAPI, CMA3 and FISH) were applied in order to analyze the structure and variability of NORs in the fish species Steindachneridion melanodermatum and S. scripta. Ag-NORs were observed on the short arm of the first acrocentric chromosome pair, coincidentally with a strong C-positive band on a large secondary constriction. In addition, NORs showed bright fluorescent signals when stained with CMA3 and treated for FISH with rDNA 18S. However, they showed negative coloration after G- and restriction enzyme banding and DAPI staining. The results evidence a substantial size polymorphism in these regions. The NOR bearing chromosomes in both species may be considered homologues because they maintain conserved characteristics, such as being interspersed with a GC-rich heterochromatin and possessing target sequences for AluI, BamHI and EcoRI.
authors.affiliation: Universidade Estadual de Londrina, Centro de Ciencias Biológicas, Caixa Postal 6001, 86051-970 Londrina, Paraná, Brasil. swarca@uel.br
authors.forename: Ana Cláudia
authors.initials: AC
authors.lastname: Swarça
authors.forename: Alberto Sérgio
authors.initials: AS
authors.lastname: Fenocchio
authors.forename: Marta Margarete
authors.initials: MM
authors.lastname: Cestari
authors.forename: Ana Lucia
authors.initials: AL
authors.lastname: Dias
mesh_terms: D000818:Animals; D002397:Catfishes / Q000235:genetics*; D002875:Chromosomes / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D007211:Indoles; D009697:Nucleolus Organizer Region / Q000235:genetics*; D016622:Silver Staining
chemical_list: D007211:Indoles; C007293:DAPI