Tetranematichthys wallacei, Vari & Ferraris, 2006, Vari & Ferraris, 2006

Casarotto, Cleisson de Cristo, Haerter, Chrystian Aparecido Grillo, Perin, Diana Paula, Jesus, Letícia Marchiotti de, Antoniazzi, Gabrielle Jovana, Blanco, Daniel Rodrigues, Treco, Fernando Rodrigo, Margarido, Vladimir Pavan, Traldi, Josiane Baccarin & Lui, Roberto Laridondo, 2024, Are the chromosomal fusions that shaped the karyotype of Tetranematichthys wallacei (Siluriformes: Auchenipteridae) a shared feature among Ageneiosini species?, Neotropical Ichthyology 22 (2), pp. e 240015-e 240015 : e240015-240015

The diploid number observed for

T. wallacei

was 2n = 52 chromosomes (32m + 18sm + 2st, NF = 104), with no differences between the sexes ( Fig. 2A ). Most heterochromatic blocks appeared pale and were located at the terminal regions; however, some pericentromeric blocks were also observed in pairs 2m, 6m, and 17sm, and centromeric blocks were evident in pairs 1m, 4m, 5m, 18sm, and 20sm ( Fig. 2B ). Fluorescent in situ hybridization (FISH) with 18S rDNA probes revealed markings at the terminal positions on the long arm of pair 17sm in all analyzed specimens ( Fig. 3A ). Additionally, three individuals (two males and one female) exhibited an additional 18S rDNA site on a single chromosome of pair 7m, located at the terminal position of its short arm ( Fig. 3A , in box). No specimen in our sample exhibited two pairs completely marked (four chromosomes) with the 18S rDNA probes. The AgNORs were coincident with the 18S rDNA sites on pair 17 ( Fig. 2A , in box). FISHs with 5S rDNA probes showed this cistron is located at the proximal position of the short arm at the pairs 8m and 10m ( Fig. 3A ). FISH with the telomeric sequence (TTAGGG) n revealed markings exclusively at the terminal regions, with no presence of interstitial telomeric sites (ITS) ( Fig. 3B ).

Figures

FIGURE 2 | A. Karyotype of Tetranematichthys wallacei Stained with Giemsa; and B. Karyotype of T. wallacei sequentially submitted to C-banding. AgNORs presented in the box. Scale bar = 10 µm.

FIGURE 3 | A. Karyotype of Tetranematichthys wallacei hybridized with 18S rDNA (green signal in pair 17) and 5S rDNA (red signal in pairs 8 and 10) probes, counterstained with DAPI. The 18S rDNA polymorphism, represented by an additional chromosome carrying the 18S rDNA sites (pair 7) are presented in the box. B. Methaphase plate of T. wallacei hybridized with telomeric probes under 77% of stringency. Scale bars = 10 µm.