Post-zygotic modifications and intra- and inter-individual nucleolar organizing region variations in fish: report of a case involving Leporinus friderici.
Silver nitrate staining, a rapid and efficient method, has proven to be excellent for nucleolar organizing region (NOR) studies in fish. Some fish appear to have only two NOR-bearing chromosomes in their karyotype, whereas others probably have several. In the present study we analyzed the NORs of Leporinus friderici, a species that, on the basis of previous studies, has been considered as representative of species with NORs carried by a single chromosome pair. The analyses were performed by a combination of three methods, i.e. silver nitrate staining, staining with the GC-specific fluorochrome chromomycin A3, and in situ hybridization with digoxigenin-labeled probes. The results showed that, although more frequent and conspicuous in a single chromosome pair, the NORs of this species are present in multiple chromosomes. Intra- and inter-individual variations observed by the three methods strongly suggest the occurrence of post-zygotic modifications involving NORs. NOR identification in fish, almost exclusively performed by the silver nitrate method, is currently being re-evaluated by methods such as chromomycin A3 staining and in situ hybridization, which may provide important information leading to a better understanding of chromosome evolution in these animals.
Galetti
P M
PM
Department of Genetics and Evolution, Federal University of São Carlos, Brazil.
Mestriner
C A
CA
Monaco
P J
PJ
Rasch
E M
EM
D000818:Animals; D002871:Chromosome Banding; D005399:Fishes / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D009697:Nucleolus Organizer Region / Q000648:ultrastructure*; D012835:Silver Nitrate; D016622:Silver Staining
D012835:Silver Nitrate