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. 2022 May 5;16(2):127-142.
doi: 10.3897/CompCytogen.v16i2.72190. eCollection 2022.

Karyotype description and comparative chromosomal mapping of rDNA and U2 snDNA sequences in Eigenmannialimbata and E.microstoma (Teleostei, Gymnotiformes, Sternopygidae)

Cristian Andrés Araya-Jaime  1 , Duílio Mazzoni Zerbinato de Andrade Silva  2 , Luís Ricardo Ribeiro da Silva  2 , Cristiano Neves do Nascimento  2 , Claudio Oliveira  2 , Fausto Foresti  2
Affiliations

Karyotype description and comparative chromosomal mapping of rDNA and U2 snDNA sequences in Eigenmannialimbata and E.microstoma (Teleostei, Gymnotiformes, Sternopygidae)

Cristian Andrés Araya-Jaime et al. Comp Cytogenet. .

Abstract

The genus Eigenmannia Jordan et Evermann,1896 includes electric fishes endemic to the Neotropical region with extensive karyotype variability and occurrence of different sex chromosome systems, however, cytogenetic studies within this group are restricted to few species. Here, we describe the karyotypes of Eigenmannialimbata (Schreiner et Miranda Ribeiro, 1903) and E.microstoma (Reinhardt, 1852) and the chromosomal locations of 5S and 18S rDNAs (ribosomal RNA genes) and U2 snDNA (small nuclear RNA gene). Among them, 18S rDNA sites were situated in only one chromosomal pair in both species, and co-localized with 5S rDNA in E.microstoma. On the other hand, 5S rDNA and U2 snRNA sites were observed on several chromosomes, with variation in the number of sites between species under study. These two repetitive DNAs were observed co-localized in one chromosomal pair in E.limbata and in four pairs in E.microstoma. Our study shows a new case of association of these two types of repetitive DNA in the genome of Gymnotiformes.

Keywords: Electric fish; fish cytogenetics; freshwater fishes; karyotype evolution; repetitive DNA.

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Figures

Figure 1.
Figure 1.
Location of Eigenmannia species in the Amazon and São Francisco basins.
Figure 2.
Figure 2.
Chromosomes stained with Giemsa and C-banded a, b karyotype and C-banded metaphase of E.limbatac, d karyotype and C-banded metaphase of E.microstoma. Scale bar: 10 μm.
Figure 3.
Figure 3.
Karyotypes of Eigenmannia species after FISH with 5S (red) and 18S (green) ribosomal DNA probes and counterstained with DAPI. Scale bar: 10 μm.
Figure 4.
Figure 4.
Karyotypes of Eigenmannia species after FISH with 5S rDNA (red) and U2 snDNA (green) probes and counterstained with DAPI. Note that, the two repetitive DNAs are located adjacently on the same pair (14) in E.limbata and they are located adjacently on four chromosome pairs (10, 12, 16 and 17) in E.microstoma. Scale bar: 10 μm.
Figure 5.
Figure 5.
Idiogram of Eigenmannia species showing the location of repetitive DNAs.
See this image and copyright information in PMC

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