Localization of ribosomal genes in three Pimelodus species (Siluriformes, Pimelodidae) of the São Francisco River: 5S genes as species markers and conservation of the 18S rDNA sites

Abstract

Pimelodidae is one of the most representative of Neotropical catfish families. However, these fish are still poorly studied in terms of cytogenetics, especially regarding the application of more accurate techniques such as the chromosomal localization of ribosomal genes. In the present work, fluorescent in situ hybridization with 5S and 18S rDNA probes was employed for rDNA site mapping in Pimelodus sp., P. fur and P. maculatus from the São Francisco River in the Três Marias municipality - MG. The results from the application of the 18S probe confirmed the previous data obtained by silver nitrate staining, identifying a simple nucleolar organizing region system for these species. However, the labeling results from the 5S rDNA probe demonstrated a difference in the number and localization of these sites between the analyzed species. The obtained data allowed inferences on the possible processes involved in the karyotypic evolution of this genus

Cytogenetic analysis of the 18S, 5S rDNA and B chromosome of Iheringichthys labrosus (Lütken, 1874) (Siluriformes, Pimelodidae)

“…The 5S rDNA location was different from that of the population studied herein, because the 5S ribosomal cistrons were in a terminal position on the long arm of a subtelocentric pair. The use of the 18S rDNA probe has been growing in the family Pimelodidae, confirming data obtained with silver nitrate, as observed in Pinirampus pirinampu (Spix and Agassiz, 1829) (Swarça et al, 1999), Zungaro zungaro (Humboldt, 1821) (Swarça et al, 2001), in different species of the genus Pimelodus (Souza et al, 2004;Garcia and Moreira-Filho, 2008), in Pseudoplatystoma corruscans (Spix and Agassiz, 1829) (Swarça et al, 2005), in Steindachneridion melanodermatum Garavello, 2005 and Steindachneridion scriptum (Miranda Ribeiro, 1918) (Swarça et al, 2008). In P. corruscans the 5S rDNA probe has been used in addition to the 18S rDNA showing that these regions are also present on different chromosomes in this species and located in a subterminal region (Swarça et al, 2005).…”

Chromosomal analyses in Megalonema platanum (Siluriformes: Pimelodidae), an endangered species from South American rivers

“…2c) as also observed in some Pimelodidae species by different authors: Souza et al (2004), Carvalho & Dias (2007), Swarça et al (2008), Garcia & Moreira Filho (2008). CMA 3 staining on chromosomes of M. platanum displayed fluorescent signals on the short arm of a pair of sm chromosomes (Fig.…”

Comparative application of direct sequencing, PCR-RFLP, and cytogenetic markers in the genetic characterization of Pimelodus (Siluriformes: Pimelodidae) species: Possible implications for fish conservation

“…The location of 5S ribosomal genes in the population of P. maculatus from the São Francisco River (MG-Brazil) reported by Garcia and Moreira-Filho (2008) differed from the pattern in the population of Pimelodus sp. from the same locality where they were located at the terminal position on long arms of an sm chromosomal pair in the latter, which was attributed to a putative paracentric inversion by the authors.…”

“…On the other hand, the data available for the genus Pimelodus indicate that the number of chromosomes bearing such genes is variable, ranging from 4 (P. fur) to 6 (P. maculatus and Pimelodus sp) (Garcia and Moreira-Filho, 2008). It should be pointed out that the populations/species from the Upper Paraná Basin differ from Pimelodus collected in the São Francisco River, mainly because of their lower number of 5S rDNA sites.…”

“…Instead, the Siluriformes species that were analyzed so far show the trend of a terminal 5S rDNA location, particularly in those species with high chromosomal numbers (Garcia and Moreira-Filho, 2008). However, this tendency will eventually be confirmed or refuted as the number of studies using such markers in this fish group increases.…”