Chromosome spreading of the retrotransposable Rex-1 and Rex-3 elements and 5S rDNA clusters in the karyotype of Eigenmannia catira (Gymnotiformes: Sternopygidae)

Lucas Pietro Ferrari Gianini¹, Ana Carolina Neiva de Oliveira², Wagner Correia³ and Carlos Alexandre Fernandes^1,4

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Abstract​

Introduction​

Gymnotiformes is an order of fish found in the Neotropical region, consisting of approximately 273 valid species divided into five families: Apteronotidae, Sternopygidae, Gymnotidae, Hypopomidae, and Rhamphichthydae (Fricke et al., 2024). Gymnotiformes are popularly known as “electric fish,” a term derived from their peculiar characteristic of continuous emission of weak electrical discharges. This unique feature serves the function of localization and communication, particularly in their nocturnal habits (Alves-Gomes, 2001). The Sternopygidae family consists of five genera: Archolaemus Korringa, 1970, Distocyclus Mago-Leccia, 1978, Eigenmannia Jordan & Evermann, 1896, Rhabdolichops Eigenmann & Allen, 1942, and Sternopygus Müller & Troschel, 1846. This family is found in all South American countries except Chile (Fricke et al., 2024). Eigenmannia, which is the most diverse genus in Sternopygidae, has 32 valid species (Fricke et al., 2024), with the highest diversity found in the Amazon basin (Dagosta, de Pinna, 2019).

In Eigenmannia, even though in recent decades there has been a considerable increase in taxonomic contributions, the genus continues with its taxonomy based on groups of species, in which the separation between individuals is made by the body morphological pattern, a condition found in several groups of fish with Neotropical distribution, as they have little phenotypic diversity and wide geographic distribution (Alves-Gomes et al., 1995; Albert, Campos, 1998; Albert, 2001; Albert, Crampton, 2003; Tagliacollo et al., 2016). The differences in the morphological pattern alternate between having an evident upper medial dark stripe, which extends along the body axis (E. trilineata complex with 16 species), individuals measuring 300 mm or more, with a vast and opaque body in life, with absence of longitudinal stripes (E. humboldtii complex with three species) and translucent white/yellowish coloration in life, with absent longitudinal stripes, large eye and long caudal filament in E. macrops (Boulenger, 1897) (Peixoto et al., 2015; Waltz, Albert, 2017, 2018 ). Eigenmannia catira Cardoso & Dutra, 2023 is one of 16 species in the E. trilineata complex, distinguished from all its congeners by a unique combination of morphometrics, meristics, osteological characters, a significant COI genetic divergence, and its karyotype (Cardoso, Dutra, 2023).

The Eigenmannia genus, known for its rich diversity, exhibits marked variability in its chromosome structure. The diploid numbers range from 2n = 28 in E. guairaca Peixoto, Dutra & Wosiacki, 2015 (Sene et al., 2014) to 2n = 38 in species such as E. virescens (Velenciennes, 1836) (Fernandes et al., 2020), E. dutrai Peixoto, Pastana & Balen, 2021 (Sene et al., 2014), E. limbata (Shreiner & Miranda Ribeiro, 1903), and E. microstomus (Reinhardt, 1852) (Araya-Jaime et al., 2022). These variations, which may or may not include sex chromosomes, such as sex chromosome XX/XY (Almeida-Toledo et al., 2002) and ZZ/ZW (Almeida-Toledo et al., 2001; Silva et al., 2009; Fernandes et al., 2020) in E. virescens, and sex chromosome ZZ/Z0 type in E. aff. trilineata López & Castello, 1966 (Araya-Jaime et al., 2017), add to the diversity of this genus. The observation of multiple sex chromosome systems, such as X₁X₁X₂X₂/X₁X₂Y in E. guairaca (Almeida-Toledo et al., 1988; Fernandes et al., 2010; Sene et al., 2014), and ZW₁W₂/ZZ in E. aff. desantanai Peixoto, Dutra & Wosiacki, 2015 (Araújo et al., 2023), further enriches our understanding of this diverse genus.

In this genus, the distribution pattern of constitutive heterochromatin appears to be conserved in populations from the same locality, primarily located in pericentromeric regions of most chromosomes (Almeida-Toledo et al., 1996; Silva et al., 2009; Sene et al., 2014; Fernandes et al., 2020; Araya-Jaime et al., 2022; Araújo et al., 2023). Nucleolar organizing regions have been identified in only one chromosome pair, characterized as a system of simple NORs (Almeida-Toledo et al., 1996; Sene et al., 2014; Fernandes et al., 2020; Araya-Jaime et al., 2022), except in Eigenmannia sp.1, which presented a system of multiple NORs (Almeida-Toledo et al., 1996). The presence of multiple 5S rDNA sites on different chromosomes is evident in E. virescens (Fernandes et al., 2020), E. microstomus, E. limbata (Araya-Jaime et al., 2022), E. guairaca, E. catira, and E. dutrai (Sene et al., 2014), suggesting a possible association with transposable elements (Sene et al., 2014). Conversely, the mapping of Rex-1 and Rex-3 retroelements was conducted in a few species of Eigenmannia, revealing their distribution in small clusters in both the euchromatic and heterochromatic portions of the studied genomes (Sene et al., 2015). The retrotransposable elements Rex-1 and Rex-3 were mapped in several fish species (review in Carducci et al., 2018). However, there still needs to be more information about the distribution pattern of these elements in Gymnotiformes, especially considering their potential role in the dispersion of other repetitive elements (Cioffi et al., 2009; Pansonato-Alves et al., 2013; Prizon et al., 2018).

In order to enhance our understanding of the chromosomal structure and the behavior of repetitive DNA sequences in the Eigenmannia genome, we are pleased to present the karyotype and chromosomal localization of four repetitive DNA classes (18S and 5S rDNA, retrotransposable Rex-1, and Rex-3 elements) in E. catira from the upper Paraná River basin. Our findings reveal a new instance of chromosome spreading of the 5S rDNA clusters in Gymnotiformes, which could be attributed to the synteny of Rex-1 and Rex-3 elements with chromosomes carrying 5S rDNA.

Material and methods

Study and sampling area. A total of twenty-five (7 females and 18 males) individuals of E. catira (Gymnotiformes, Sternopygidae) were obtained from the Iguatemi River (Fig. 1A), located in the municipality of Mundo Novo, Mato Grosso do Sul, Brazil (23°89’52.78”S 54°25’91.67”W). Voucher specimens were deposited in the fish collection at the Universidade Estadual de Maringá, Brazil, as E. catira (NUP 25154) (Fig. 1B).

FIGURE 1| The Iguatemi River (A) is located in the upper Paraná River basin, where individuals of Eigenmannia catira were captured in Mato Grosso do Sul, Brazil. The dark square indicates the sampling point. Specimen of E. catira collected (B), scale bar = 1 cm.

Cytogenetic analysis. Metaphase chromosomes were obtained from anterior kidney cells using the air-drying technique (Bertollo et al., 2015). The nucleolar organizer regions (NORs) were detected employing silver nitrate staining (Howell, Black, 1980). Heterochromatin was determined following the C-banding technique (Sumner, 1972) and stained with propidium iodide (Lui et al., 2012).

At least 30 metaphases were analyzed for each individual, and those with better chromosome morphology were used for the karyotype analysis. The chromosomes were classified as metacentric (m), submetacentric (sm), subtelocentric (st), and acrocentric (a) according to (Levan et al., 1964). The fundamental number (FN) was calculated according to the chromosomal arm numbers (the chromosomes m, sm, and st were considered to contain two arms – p and q arms – and the a with one arm – only q arm).

The location of the 5S and 18S rDNA sites in the chromosomes was performed by fluorescence in situ hybridization (FISH) with modifications (Margarido, Moreira-filho, 2008; Pinkel et al., 1986) using probes from the genome of Megaleporinus elongatus (Valenciennes, 1850) (Martins, Galetti Jr., 1999) and Prochilodus argenteus Spix & Agassiz, 1829 (Hatanaka, Galetti Jr., 2004), respectively. The probes were labeled through nick translation with digoxigenin-11-dUTP (5S rDNA) and biotin-16-dUTP (18S rDNA) (Roche). Detection and amplification of the hybridization signal were carried out using avidin-FITC and anti-avidin biotin (Sigma) for probes labeled with biotin and anti-digoxigenin rhodamine (Roche) for probes labeled with digoxigenin. Chromosomes were counterstained with DAPI (50 μg ml⁻¹).

Transposable element probes were produced using the primers Rex-3 [Foward (5’- CGGTGAYAAAGGGCAGCCCTG-3’) and Reverse (5’-TGGCAGACNGGGGTGGTGGT-3’) (Volff, 2006). REX-1 [Foward (5’- TTCTCCAGTGCCTTCAACACC-3’) and Reverse (5’ – TCCCTCAGCAGAAAGAGTCTGCTC-3’) (Volff et al., 1999). Amplification was performed using PCR, and the probes were labeled according to the nick translation method using the Anti-digoxigenin-Rhodamine Kit (Roche). Chromosomes were counterstained with DAPI (50 μg ml−1).

Conventional and fluorescence chromosome preparations were analyzed under an epifluorescence microscope (Olympus BX51). The images were captured using the DP controller (Media Cybernetics) software and the image composition with Adobe Photoshop CS6.

Results​

All individuals of Eigenmannia catira had 36 chromosomes with a karyotype composed of 2 metacentric + 10 submetacentric + 8 subtelocentric + 16 acrocentric chromosomes, with a fundamental number (FN) equal to 56 for both sexes (Fig. 2A). No heteromorphic sex chromosomes were identified. Using silver nitrate impregnation, it was revealed that the Ag-NORs were located at the terminal region of the short arms in the last pair of subtelocentric chromosomes (pair 10), which coincided with the secondary constriction (Box in the Fig. 2A).

FIGURE 2| Eigenmannia catira karyotypes stained with Giemsa (A), C-banding (B), and after double FISH with 18S rDNA (in green) and 5S rDNA (in red) probes (C). The highlighted box contains the pair carrying the nucleolar organizing region after impregnation with silver nitrate. Scale bar = 10 µm.

Heterochromatin was primarily found in the pericentromeric regions of most chromosomes, with a significant accumulation of heterochromatin at the sites of Ag-NORs and at the terminal regions of the long arms in pairs 9 and 11 (Fig. 2B).

The FISH technique using the 18S rDNA probe confirmed the labeling obtained by silver nitrate and did not detect any additional inactive major ribosomal clusters (Figs. 2C, 3). Multiple 5S rDNA sites were observed in the pericentromeric position in 21 chromosomes (Figs. 2C, 3), being that in pair 2 only one of the homologues presented marking. In the FISH experiments, small clusters of the Rex-1 and Rex-3 elements were observed dispersed throughout the chromosomes, spanning both euchromatic and heterochromatic regions (Fig. 3). However, despite employing identical experimental hybridization conditions in all assays, the Rex-1 element appears to be more abundant than Rex-3.

FIGURE 3| Eigenmannia catira karyotypes comparing double FISH with 18S (in green) and 5S (in red) rDNA probes, FISH with Rex-1, Rex-3 probes, and C-banding (Het). Scale bar = 10 µm.

Discussion​

The karyotype of Eigenmannia catira analyzed in the present study showed that the morphology pattern of the chromosomes, C-banding, 5S and 18S rDNA differed from the patterns previously described for the species (Sene et al., 2014). The patterns of chromosomal morphology found in E. catira containing 2m + 10sm + 8st + 16a obtained here have never been observed in other populations of this species (Tab. 1). According to Cardoso, Dutra (2023), only one karyotypic analysis of the species, previously identified as Eigenmannia sp., has been carried out to date (Sene et al., 2014). In this study, the individuals from Hortelã River (upper Paraná River basin) had same diploid number (2n = 36), but 8m/sm + 28st/a (Sene et al., 2014), while in the present study 12m/sm +24st/a. It is important to note that despite the maintenance of the diploid number, rearrangements modifying the chromosomal morphology, such as pericentric inversions, have played a significant role in the karyotypic evolution of E. catira.

TABLE 1 | Cytogenetic data of species in Eigenmannia, species name following Cardoso, Dutra (2023). ¹Previously mentioned as Eigenmannia sp.1, ²previously mentioned as E. trilineata, ³previously mentioned as Eigenmannia sp.2, ⁴previously mentioned as E. virescens, ⁵previously mentioned as E. virescens-XY, p = short arm. q = long arm. T = terminal region. I = interstitial region. 5S rDNA = number of carrier chromosomes, Ag-NORs/18S rDNA = carrier pair.

The terminal location of NORs on the short arm of the last pair of subtelocentric chromosomes, as revealed by our unique research using silver impregnation and FISH with the 18S rDNA probe, is a significant discovery. This finding, similar to that previously described in E. catira (Sene et al., 2014), confirms a simple NORs for this species. Simple NORs, a shared feature among Eigenmannia species, are predominantly located in the terminal portion of short arms (p) of subtelo/acrocentric chromosomes (Tab. 1). This fact, described for Eigenmannia, seems to also occur in another genus of Gymnotiformes; Milhomem et al. (2013) showed that despite the occurrence of high karyotypic variability in Gymnotus species, the NOR-bearing chromosomes are homeologous in different species (G. inaequilabiatus (Valenciennes, 1839), G. pantherinus (Steindachner, 1908) and G. cf. carapo Linnaeus, 1758), showing to be conserved in most species of this order. On the other hand, E. guairaca (previously cited as Eigenmannia sp.1 (2n = 28) and Eigenmannia sp.2 (2n = 31/32) by Sene et al., 2014 and as E. trilineata by Fernandes et al., 2010) and E. aff. desantanai (Araújo et al., 2023) are the only two species that presents NORs located in the interstitial position, possibly indicating that pair 10 of these species may have arisen through fusion events involving ancestral chromosomes carrying ribosomal sequences.

The research findings indicate that the heterochromatin regions are present in all chromosomal pairs, with the majority being located in the pericentromeric regions. Only two pairs exhibit terminal markings on the long arms of subtelocentric and acrocentric chromosomes. A prior study of E. catira also observed similar heterochromatin patterns, with at least four chromosomal pairs showing terminal markings on the long arms of subtelocentric and acrocentric chromosomes (Sene et al., 2014). Furthermore, in the current study, the heterochromatic regions aligned with the 5S rDNA sites in most chromosomes, with the exception of pair 9, resembling the pattern observed in E. catira (Sene et al., 2014), as well as in other Eigenmannia species such as E. virescens (Fernandes et al., 2020) and E. microstomus (Araya-Jaime et al., 2022). Conversely, other species such as E. limbata, E. guairaca, and E. cf. trilineata showed a lower number of coinciding chromosomes with heterochromatic regions (Sene et al., 2014; Araya-Jaime et al., 2022).

The physical mapping of 5S rDNA in the E. catira genome showed these sites located on 21 chromosomes and non-syntenic with the 18S rDNA sites, a characteristic also previously observed in E. catira, but with only six chromosomes carrying 5S rDNA (Sene et al., 2014). Multiple 5S rDNA sites appear to be a characteristic among other Eigenmannia species (Tab. 1), except in E. guairaca with a sexual system of the X₁X₁X₂X₂/X₁X₂Y type, which presented only two chromosomes carrying these cistrons (Sene et al., 2014).

One possible hypothesis to account for the increased dispersion of copies of the 5S rDNA genes in E. catira is the potential use of a mechanism involving the spread of retrotransposons by the ribosomal DNA. This hypothesis finds support in the synteny of Rex-1 and Rex-3 elements present in pairs carrying the 5S rDNA described here. In the E. catira population described by Sene et al. (2015), the discrete presence of blocks marked with Rex-1 and Rex-3 on the chromosomes may explain the lower number of chromosomes carrying 5S rDNA (6) compared to the E. catira population under study here (21). As a result, these elements could potentially be a contributing factor to the numerical variation in 5S rDNA sites between these two populations.

The Rex-1 and Rex-3 retrotransposons analyzed here showed a dispersed pattern throughout all chromosomes, and synteny with heterochromatin, euchromatin, and 5S rDNA regions, with Rex-1 having more abundant than Rex-3. Similarly, Sene et al. (2015) showed that the Rex-1 and Rex-3 transposable elements in E. guairaca, E. dutrai, E. cf. trilineata, and E. catira, are also organized into small clusters, including euchromatic and heterochromatic regions. However, in this study, Rex-3 elements are more abundant than Rex-1 elements, as well as more concentrated in the sexual chromosomes X₁ and X₂ of E. guairaca and in the X chromosome of E. dutrai¸ suggesting that Rex-3 played an essential role in the process of differentiation of the sex chromosomes of these species.

The available data is instrumental in gaining insight into the karyotypic evolution of Eigenmannia. Pericentromeric inversions are chromosomal rearrangements that are crucial in distinguishing karyotypes of E. catira. The data on NORs in E. catira confirm Eigenmannia tendency to have simple NOR sites. Multiple 5S rDNA sites across various E. catira chromosomes can be attributed to the synteny of Rex-1 and Rex-3 elements with chromosomes carrying 5S rDNA. These transposable elements may have played a vital role in spreading this ribosomal DNA within the genome of this species.

Acknowledgments​

We thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), through the Dean of the Postgraduate and Research Department of the Universidade Estadual de Maringa (UEM-PPG), for the master’s scholarship granted to LPFG.

References​

Albert JS, Campos DPR. Phylogenetic systematics of Gymnotiformes with diagnoses of 58 clades: a review of available data. In: Malabarba LR, Reis RE, Vari RP, Lucena ZM, Lucena CA, editors. Phylogeny and classification of Neotropical fishes. Porto Alegre: Edipucrs; 1998. p.419–46.

Albert JS. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Mis Pub Mus Zool UM. 2001; 190:1–127. Available from: https://deepblue.lib.umich.edu/handle/2027.42/56433

Albert JS, Crampton WGR. Seven new species of the Neotropical electric fish Gymnotus (Teleostei, Gymnotiformes) with a redescription of G. carapo (Linnaeus). Zootaxa. 2003; 287(1):1–54. https://doi.org/10.11646/zootaxa.287.1.1

Almeida-Toledo LF, Viegas-Péquignot E, Foresti F, Toledo-Filho SA, Dutrillaux B. BrdU replication patterns demonstrating chromosome homoeologies in two fish species, genus Eigenmannia. Cytogenet Cell Genet. 1988; 48(2):117–20. https://doi.org/10.1159/000132603

Almeida-Toledo LF, Stocker AJ, Foresti F, Toledo-Filho SA. Fluorescent in situ hybridization with rDNA probes on chromosomes of two nucleolus organizer region phenotypes of a species of Eigenmannia (Pisces, Gymnotoidei, Sternopygidae). Chromosome Res. 1996; 4:301–05. https://doi.org/10.1007/BF02263681

Almeida-Toledo LF, Foresti F, Péquignot EV, Daniel-Silva MFZ. XX:XY sex chromosome systema with X heterochromatinization: an early stage of sex chromosome differentiation in the Neotropic electric ell Eigenmannia virescens. Cytogenet Cell Genet. 2001; 95(1–2):73–78. https://doi.org/10.1159/000057020

Almeida-Toledo LF, Daniel-Silva MFZ, Moysés CB, Fonteles SBA, Lopes CE, Akama A et al. Chromosome Evolution in fish: sex chormosome variablity in Eigenmannia virescens (Gymnotiformes: Sternoopygidae). Cytogenet Genome Res. 2002; 99(1–4):164–69. https://doi.org/10.1159/000071589

Alves-Gomes JA, Ortí G, Haygood M, Heiligenberg W, Meyer A. Phylogenetic analysis of the South American electric fish (order Gymnotiformes) and the evolution of their electrogenic system: a synthesis based on morphology, electrophysiology, and mitochondrial sequence data. Mol Biol Evol. 1995; 12(2):298–318. https://doi.org/10.1093/oxfordjournals.molbev.a040204

Alves-Gomes JA. The evolution of electroreception and bioelectrogenesis in teleost fish: a phylogenetic perspective. J Fish Biol. 2001; 58(6):1489–511. https://doi.org/10.1111/j.1095-8649.2001.tb02307.x

Araújo L, Ramos LI, Vieira M, Oliveira A, Portela-Castro A, Borin-Carvalho L et al. Cytogenetic and molecular characterization of Eigenmannia aff. desantanai (Gymnotiformes: Sternopygidae): a first report of system of sex chromosomes ZW₁W₂/ZZ in gymnotiformes. Zebrafish. 2023; 20(2):77–85. https://doi.org/10.1089/zeb.2022.0059

Araya-Jaime C, Mateussi NTB, Utsunomia R, Costa-Silva GJ, Oliveira C, Foresti F. ZZ/Z0: the new system of sex chromosomes in Eigenmannia aff. trilineata (Teleostei: Gymnotiformes: Sternopygidae) characterized by molecular cytogenetics and DNA barcoding. Zebrafish.2017; 14(5):464–70. https://doi.org/10.1089/zeb.2017.1422

Araya-Jaime C, Silva DMZA, Silva LRR, Nascimento CN, Oliveira C, Foresti F. Karyotype description and comparative chromosomal mapping of rDNA and U2 snDNA sequenes in Eigenmannia limbata and E. microstoma (Teleostei, Gymnotiformes, Sternopygidae). Comp Cytogen. 2022; 16(2):127–42. https://doi.org/10.3897/compcytogen.v16i2.72190

Bertollo L, Cioffi M, Moreira-Filho O. Direct chromosome preparation from freshwater teleost fishes, fish cytogenetic techniques. In: Ozouf-Costaz C, Pisano E, Foresti F, Toledo LFA, editors. Fish citogenetic techniques: rayfin fishes and chondrichthyans. Boca Raton: CRC Press; 2015. p.21–26. https://doi.org/10.1201/b18534-4

Cardoso VC, Dutra GM. Description of a new species of glass knifefish genus Eigenmannia (Gymnotiformes: Sternopygidae) from the upper rio Paraná basin, based on anatomical, karyotypic, and molecular evidences. Neotrop Ichthyol. 2023; 21(4):e230090. https://doi.org/10.1590/1982-0224-2023-0090

Carducci F, Barucca M, Canapa A, Biscotti MA. Rex retroelements and teleost genomes: an overview. Int J Mol Sci. 2018; 19(11):3653. https://doi.org/10.3390/ijms19113653

Cioffi MB, Martins C, Bertollo LAC. Comparative chromosome mapping of repetitive sequences. Implications for genomic evolution in the fish, Hoplias malabaricus. BMC Genet. 2009; 10:34. https://doi.org/10.1186/1471-2156-10-34

Dagosta FCP, de Pinna M. The fishes of the Amazon: distribution and biogeographical patterns, with a comprehensive list of species. Bull Am Mus Nat Hist. 2019; 2019(431):1–163. https://doi.org/10.1206/0003-0090.431.1.1

Fernandes CA, Bailly D, Silva VFB, Martins-Santos IC. System of multiple sex chromosome in Eigenmannia trilineata López & Castello, 1966 (Sternopygidae, Gymnotiformes) from Iguatemi River basin, MS, Brazil. Cytologia. 2010; 75(4):463–66. https://doi.org/10.1508/cytologia.75.463

Fernandes CA, Curiel MH, Paiz LM, Baumgärtner L, Piscor D, Margarido VP. A novel ZZ/ZW chromosome morphology type in Eigenmannia virescens (Gymnotiformes: Sternopygidae) from upper Paraná River basin. Biologia. 2020; 75:1563–69. https://doi.org/10.2478/s11756-019-00401-0

Fricke R, Eschmeyer WN, Van der Laan R. Eschmeyer’s catalog of fishes: genera, species, references. [Internet]. San Francisco: California Academy of Science; 2024. Avaliable from: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp

Griffiths SP. The use of clove oil as an anaesthetic and method for sampling intertidal rockpool fishes. J Fish Biol. 2000; 57(6):1453–64. https://doi.org/10.1111/j.1095-8649.2000.tb02224.x

Hatanaka T, Galetti Jr. PM. Mapping of the 18S and 5S ribosomal RNA genes in the fish Prochilodus argenteus Agassiz, 1829 (Characiformes, Prochilodontidae). Genetica. 2004; 122:239–44. https://doi.org/10.1007/s10709-004-2039-y

Howell WM, Black DA. Controlled silver of nucleolus organizer regions with a protective colloidal developer: a 1-step method. Experientia. 1980; 36:1014–15. https://doi.org/10.1007/BF01953855

Levan A, Fredga K, Sandberg AA. Nomenclature for centromeric position on chromosomes. Hereditas. 1964; 52(2):201–20. https://doi.org/10.1111/j.1601-5223.1964.tb01953.x

Lui RL, Blanco DR, Moreira-Filho O, Margarido VP. Propidium iodide for making heterochromatin more evidente in the C-banding technique. Biotech histochem. 2012; 87(7):433–38. https://doi.org/10.3109/10520295.2012.696700

Margarido VP, Moreira-Filho O. Karyotypic differentiation through chromosome fusion and number reduction in Imparfinis hollandi (Ostariophysi, Heptapteridae). Genet Mol Biomol. 2008; 31(1):235–38. https://doi.org/10.1590/S1415-47572008000200012

Martins C, Galetti Jr. PM. Chromosomal localization of 5S rDNA genes in Leporinus fish (Anostomidae, Characiformes). Chromosome Res. 1999; 7:363–67. https://doi.org/10.1023/A:1009216030316

Milhomem SSR, Scacchetti PC, Pieczarka JC, Fergunson-Smith MA, Pansonato-Alves JC, O’Brien PCM et al. Are NORs always located on homeologous chromosomes? A FISH investigation with DNAr and whole chromosome probes in Gymnotus fishes (Gymnotiformes). PLoS ONE. 2013; 8(2):55608. https://doi.org/10.1371/journal.pone.0055608

Pansonato-Alves JC, Serrano EA, Utsunomia R, Scacchetti PC, Oliveira C, Foresti F. Mapping five repetitive DNA classes in sympatric species of Hypostomus (Teleostei: Siluriformes: Loricariidae): analysis of chromosomal variability. Rev Fish Biol Fish. 2013; 23(4):477–89. https://doi.org/10.1007/s11160-013-9303-0

Peixoto LAW, Dutra GM, Wosiacki WB. The electric glass knifefishes of the Eigenmannia trilineata species-group (Gymnotiformes: Sternopygidae): monophyly and description of seven new species. Zool J Linn Soc. 2015; 175(2):384–414. https://doi.org/10.1111/zoj.12274

Pinkel D, Strume T, Gray JW. Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hibridization. PNAS. 1986; 83(9):2934–38. https://doi.org/10.1073/pnas.83.9.2934

Prizon AC, Bruschi DP, Gazolla CB, Borin-Carvalho LA, Portela-Castro ALB. Chromosome spreading of the retrotransposable Rex-3 element and microsatellite repeats in karyotypes of the Ancistrus populations. Zebrafish. 2018; 15(5):504–14. https://doi.org/10.1089/zeb.2018.1620

Sene VF, Pansonato-Alves JC, Utsunomia R, Oliveira C, Foresti F. Karyotype diversity and patterns of chromosomal evolution in Eigenmannia (Teleostei, Gymnotiformes, Sternopygidae). Comp Cytogen. 2014; 8(4):301–11. https://doi.org/10.3897/CompCytogen.v8i4.8396

Sene VF, Pansonato-Alves JC, Ferreira DC, Utsunomia R, Oliveira C, Foresti F. Mapping of the retrotransposable elements Rex1 and Rex3 in chromosomes of Eigenmannia (Teleostei, Gymnotiformes, Sternopygidae). Cytogenet Genome Res. 2015; 146(4):319–24. https://doi.org/10.1159/000441465

Silva DS, Milhomem SSR, Pieczarka JC, Nagamachi CY. Cytogenetic studies in Eigenmannia virescens (Sternopygidae, Gymnotiformes) and new inferences on the origin of sex chromosomes in the Eigenmannia genus. BMC Genetics. 2009; 10:74. https://doi.org/10.1186/1471-2156-10-74

Sumner AT. A simple technique for demonstrating centromeric heterochromation. Exp Cell Res. 1972; 75(1):304–06. https://doi.org/10.1016/0014-4827(72)90558-7

Tagliacollo VA, Bernt MJ, Craig JM, Oliveira C, Albert JS. Data supporting phylogenetic reconstructions of the Neotropical clade Gymnotiformes. Data in Brief. 2016; 7:23–59. https://doi.org/10.1016/j.dib.2016.01.069

Volff JN. Turning junk into gold: domestication of transposable elements and the creation of new genes in eukaryotes. BioEssays. 2006; 28( 9):913–22. https://doi.org/10.1002/bies.20452

Volff JN, Körting G, Sweeney K, Schartl M. The non-LTR retrotransposon Rex3 from the fish Xiphophorus is widespread among teleosts. Mol Biol Evol. 1999; 16(11):1427–38. https://doi.org/10.1093/oxfordjournals.molbev.a026055

Waltz BT, Albert JS. Family Sternopygidae. In: Van der Sleen P, Albert JS, editors. Field guide to the fishes of the Amazon: fish genera of the Amazon, Orinoco, & Guianas. Princeton University Press: Princeton; 2017. p.341–45.

Waltz BT, Albert JS. New species of glass knifefish Eigenmannia loretana (Gymnotiformes: Sternopygidae) from the Western Amazon. Zootaxa. 4399(3):399–411. https://doi.org/10.11646/zootaxa.4399.3.9

Authors

Lucas Pietro Ferrari Gianini¹, Ana Carolina Neiva de Oliveira², Wagner Correia³ and Carlos Alexandre Fernandes^1,4

^[1]    Programa de Pós-Graduação em Biologia Comparada, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil. (LPFG) luquindia@gmail.com, (CAF) cafernandes@uem.br (corresponding author).

^[2]    Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil. (ACNO) ra119066@uem.br.

^[3]    Centro Educacional de Mundo Novo, Av. Filinto Muller, 1694, 79980-000, Mundo Novo, MS, Brazil. (WC) vavabiomsn@hotmail.com.

^[4]    Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura (Nupelia) – Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá, PR, Brazil.

Authors’ Contribution

Lucas Pietro Ferrari Gianini: Data curation, Formal analysis, Methodology, Validation, Visualization, Writing-original draft, Writing-review and editing.

Ana Carolina Neiva de Oliveira: Formal analysis, Methodology, Writing-review and editing.

Wagner Correia: Methodology, Writing-review and editing.

Carlos Alexandre Fernandes: Conceptualization, Data curation, Formal analysis, Methodology, Project administration, Validation, Visualization, Writing-original draft, Writing-review and editing.

Ethical Statement​

This study was carried out strictly following the recommendations of the Guide for the Care and Use of Laboratory Animals, approved by the Animal Experimentation Ethics Committee of the Universidade Estadual de Maringá (License Number: nº 6792170120 – CEUA/UEM). The experiments followed ethical conduct, and before euthanasia, the fish were anesthetized with an overdose of clove oil (Griffiths, 2000). The animals were captured with authorization from the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio, number 73763–42).

Competing Interests

The author declares no competing interests.

How to cite this article

Gianini LPF, Oliveira ACN, Correia W, Fernandes CA. Chromosome spreading of the retrotransposable Rex-1 and Rex-3 elements and 5S rDNA clusters in the karyotype of Eigenmannia catira (Gymnotiformes: Sternopygidae). Neotrop Ichthyol. 2025; 23(1):e240072. https://doi.org/10.1590/1982-0224-2024-0072

Copyright​

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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