Ribosomal genes in Coregonid fishes (Coregonus lavaretus, C. albula and C. peled) (Salmonidae): single and multiple nucleolus organizer regions

Abstract

Major rDNA loci, i.e. nucleolus-organizing regions (NORs), were assigned using chromomycin-A3 (CMA3) staining followed by sequential silver (Ag) staining and in situ hybridization (ISH) with a rDNA probe to the chromosomes of the European whitefish (Coregonus lavaretus), the peled (Coregonus peled) and the vendace (Coregonus albula), three closely related coregonine salmonid fishes. One pair of NOR-bearing chromosomes was found in the peled karyotype. Multichromosomal, but stable, locations of rDNA sites on three pairs of chromosomes were observed in the European whitefish karyotype. Multichromosomal polymorphic locations, both in site and number, were observed in the karyotype of the vendace. Several Ag-, CMA3- and ISH-positive regions were found which defined up to seven cytotypes of five NOR-bearing chromosomes. All positive Ag-NORs detected corresponded both to rDNA-ISH- and CMA3-positive signals, which suggests extensive structural polymorphism in the locations of rDNA sites. Stable NOR sites were found at the same location on both homologous elements of the chromosome no. 9 in all individuals, while the remaining NORs were quite variable between individuals, and often present in heterozygous condition. The apparently similar and parallel evolutionary rDNA differentiation patterns in the subfamilies Coregoninae and Salmoninae (family Salmonidae) are observed and discussed.

Lack of correspondence between CMA₃-, Ag-positive signals and 28S rDNA loci in two Iberian minnows (Teleostei, Cyprinidae) evidenced by sequential banding

“…In some cases such relation is merely presumed, i.e. in coregonid species Jankun et al (2001) found the same number of CMA 3 -stained sites and FISH signals on apparently the same chromosome pairs. From then on the authors assumed a positive correlation (Jankun et al, 2003b).…”

“…It is commonly accepted that major rDNA clusters on fish chromosomes can also be identified by fluorescent staining with chromomycin antibiotic (CMA 3 ) that binds preferentially to GC-rich chromatin segments characteristic of rDNA sites of teleostean fishes (e.g., Mayr et al, 1985;Amemiya and Gold, 1986;Schmid and Guttenbach, 1988). Correlations between Ag-NORs and CMA 3 positive sites have been reported for several fish species (e. g., Sola et al, 2000;Jankun et al, 2001Jankun et al, , 2003aRabova et al, 2001Rabova et al, , 2003.…”

Polymorphisms of the nucleolus organizing regions in Loricaria cataphracta (Siluriformes, Loricariidae) of the upper Paraguay River basin indicate an association with transposable elements

“…Polymorphisms of the NOR are relatively common in fish, especially in the Salmonidae and Characidae families, which show both intra-and inter-individual variation of these regions (Galetti Jr., 1998;Castro et al, 1996Castro et al, , 2001Jankun et al, 2001;Santi-Rampazzo et al, 2008). Although inter-individual variations of NORs are considered to be relatively rare in fish, some have been identified in Leporinus friderici (Galetti Jr. et al, 1995), Serrapinnus notomelas (Santi-Rampazzo et al 2008), in the genus Symphysodon (Gross et al, 2010), R. lanceolata (Porto, 2012), and in L. cataphracta (present study).…”

Comparative FISH analysis in five species of Eyprepocnemidine grasshoppers

“…This suggests that the ancestral number of rDNA clusters in the Eyprepocnemidinae is restricted to one to three of the four smallest autosomes (M 8 -S 11 ). In some animal groups, for example, fishes, the existence of a single rDNA cluster is considered a plesiomorphic character (see Jankun et al, 2001), although many examples of multichromosomal location of rDNA have been described (see Castro et al, 2001). In the Eyprepocnemidinae grasshoppers analysed here, the most conserved rDNA cluster is that located on the S 9 chromosome, which is present in four of the five species analysed.…”