PACHECO, Rosiley Berton. Análise citogenética em duas espécies do gênero
Astyanax de diferentes bacias hidrográficas: localização dos genes
ribossômicos 18S e 5S. 2008. 55p. Tese (Doutorado em Ciências Biológicas –
Área de Concentração, Biologia Celular e Molecular) – Universidade Estadual de
Maringá.
ABSTRACT
A cytogenetic study was conducted on specimens of two species of Astyanax in
Brazil. A. jacuhiensis whose type-locality is Jacuhy, RS, was collected at three
different points in the Guaíba stream basin: Gasômetro, Arroio do Ribeiro and Barra
do Ribeiro. A. altiparanae was obtained from three different localities: Monjolinho
river (Monjolinho river basin/SP), Água dos Patos river (Paranapanema river
basin/SP) and Igapó stream (Tibagi river basin/PR). All of the specimens of A.
jacuhiensis showed a diploid number of 50 chromosomes with a karyotype of
8m+30sm+4st+8a (NF=92). All the populations of A. altiparanae also had a
chromosome number of 2n=50, but with different karyotype formulas: the population
of the Monjolinho river with 10m, 28sm, 4st and 8a (NF=92), that of the Água dos
Patos river with 8m, 24sm, 6st and 12a (NF=88) and the population of Igapó stream
with 8m, 28sm, 4st and 10a (NF=90). Using the AgNOR technique in the two
species, a variation of 1 to 5 nucleolar chromosomes was demonstrated, showing
localization in the telomeric regions of the short arm of different chromosomes along
with size heteromorphism. Meanwhile, using fluorescence in situ hybridization (FISH)
with an 18S rDNA probe, populations of A. altiparanae from the Monjolinho river and
Igapó stream and of A. jacuhiensis from Guaíba stream were found to have only one
chromosome pair with fluorescent staining, whereas the population from the Água
dos Patos river showed 4 fluorescent regions. FISH utilizing 5S rDNA showed one
chromosome pair with fluorescent signals in the interstitial region in A. altiparanae.
Staining with chromomycin A
3
(CMA
3
) in A. jacuhiensis and A. altiparanae
corresponded with some AgNOR sites, these being rich in GC bases. Treatment with
DAPI showed negative staining of chromosomes that were CMA
3
positive, where no
AT-rich region was observed. C banding was used only in the population of A.
jacuhiensis from Guaíba stream, and revealed heterochromatin blocks in the
pericentromeric regions in the majority of the chromosomes, where some interstitial
staining was observed, and one chromosome pair (sm) with heterochromatic staining
more evident in the terminal portion of the short arm. CB+CMA
3
in A. jacuhiensis
confirmed that the heterochromatin was associated with NORs besides other
fluorescent bands in pericentromeric and intersticial regions. These are the first
cytogenetic data for Astyanax jacuhiensis, and findings in three populations of A.
altiparanae confirm a chromosome variability in this group of fishes.