Heterochromatin analysis in the fish species Liposarcus anisitsi (siluriformes) and Leporinus elongatus (characiformes)

Abstract

The chromosomes of two neotropical freshwater fish species, namely Liposarcus anisitsi (Siluriformes, Loricariidae) and Leporinus elongatus (Characiformes, Anostomidae), were investigated by means of C-banding, Ag-NORs, fluorochrome staining and banding by hot saline solution (HSS) treatment, to reveal patterns of heterochromatin differentiation. The karyotype of L. anisitsi is described for the first time. Staining with the GC-specific fluorescent antibiotic mithramycin (MM) revealed bright signals in some C-banded blocks in both species, suggesting that these MM+ heterochromatin contains GC-rich DNA. Banding by denaturation employing HSS, followed by Giemsa staining, yielded corresponding results documenting the thermal stability of GC-rich DNA part of heterochromatin positive after C-banding. In L. elongatus the Ag-NOR also followed the above banding patterns. However, in L. anisitsi the Ag-NOR was MM+ but negatively stained after C-banding and HSS treatment. L. elongatus also showed C-banded segments that were negative for mithramycin staining and HSS treatment. The results obtained evidence the heterochromatin heterogeneity in these fish species.<br>Cromossomos mitóticos de duas especies de peixes neotropicais, Leporinus elongatus (Characiformes) e Liposarcus anisitsi (Siluriformes), foram estudados por diferentes métodos de bandamentos, com o intuito de investigar a diferenciação da heterocromatina. Enquanto que a macroestrutura cariotípica de L. elongatus já foi objeto de estudos anteriores, o cariótipo de L. anisitsi está sendo apresentado pela primeira vez. Em ambas as espécies, a coloração dos cromossomos com a mitramicina (MM), fluorocromo GC específico, evidenciou sinais brilhantes em alguns segmentos heterocromáticos também positivos ao bandamento C, sugerindo ser esta fração da heterocromatina rica em seqüências de bases GC. O tratamento dos cromossomos com solução salina aquecida e posterior coloração com Giemsa demonstrou resultados similares, documentando a estabilidade térmica do DNA rico em bases GC, presente na heterocromatina constitutiva. Em L. elongatus a Ag-NOR também seguiu os padrões de bandamentos acima. Em L. anisitsi, contudo, a Ag-NOR apresentou-se MM+ mas negativamente corada após o bandamento C e o tratamento com solução salina aquecida. Por outro lado, em L. elongatus, alguns segmentos que foram positivos ao bandamento C mostraram-se negativos à coloração com mitramicina, assim como à coloração com Giemsa após o tratamento térmico com solução salina. Os resultados obtidos evidenciam a heterogeneidade da heterocromatina no complemento cariotípico das espécies estudadas

Evolutionary cytogenetics of the Hoplias lacerdae, Miranda Ribeiro, 1908 group: a particular pathway concerning the other Erythrinidae fish

“…However, ribosomal cistrons were not detected in these four chromosomes after FISH. Similar cases in which GC-rich sites were not correlated with NORs have also been observed in few other fish, such as in species of the genus Schizodon (Martins and Galetti Jr., 1998), Liposarcus and Leporinus (Artoni et al, 1999), Eigenmannia (Almeida-Toledo et al, 2000), and some Loricariidae (Kavalco et al, 2004). According to Sumner (1990), chromosome staining with silver nitrate may also highlight argentophilic heterochromatic sites, which can explain the present results.…”

Cytogenetic analysis and chromosomal characteristics of the polymorphic 18S rDNA in the fish Prochilodus lineatus (Characiformes, Prochilodontidae)

“…The correlation of NOR sites with GC-rich sites is relatively common among fish, although staining with GC-specific fluorochromes is not considered as a method for the direct determination of ribosomal genes but of GC-rich heterochromatins associated with a gene cluster (Artoni et al, 1999). Pendás et al (1993) used in situ hybridization with 18S rDNA probes to show that the ribosomal genes of Atlantic salmon (Salmo salar) were interspersed throughout the heterochromatic chromosomal regions and that this resulted in an apparent coincidence between ribosomal genes and heterochromatic regions when the chromosomes subjected to silver nitrate staining and C-banding, these observations being supported by our results with P. lineatus (Figure 3a, e).…”

Comparative cytogenetics of Hoplias malabaricus (Pisces, Erythrinidae): a population analysis in adjacent hydrographic basins

“…It is interesting that, in the neotropical genera Leporinus, Tryportheus and Hoplias, sex chromosomes can also bear such kind of association (Molina et al, 1998;Artoni et al, 1999;Born and Bertollo, 2000;Artoni and Bertollo, 2000). In the H. malabaricus cytotype B, the X chromosome has an rDNA site in the distal region of its long arm .…”