Karyotypic characterization and genomic organization of the 5S rDNA in Erpetoichthys calabaricus (Osteichthyes, Polypteridae)

Abstract

Polypterids are a group of Osteichthyan fish whose evolutionary relationships with closer basal ray-finned and lobe-finned fish have been disputed since their discovery. Very little is known about the evolutive karyology in the whole Polypteriformes group. In order to fill this gap, a cytogenetic analysis of Erpetoichthys calabaricus species was performed, using both classical and molecular techniques. Karyotype structure (2n = 36; FN = 72), chromosome location of telomeric sequences (TTAGGG)n and ribosomal 5S and 18S rRNA genes were examined in twenty specimens of E. calabaricus by using Ag-NOR, classical C-banding, sequential CMA3/4',6-diaminidino-2-phenylindole (DAPI) staining and fluorescent in situ hybridization (FISH). CMA3 marked all centromerical and some (no. 1 and no. 15) telomeric regions. Staining with Ag-NOR and CMA3 showed the presence of two NORs on the p arm of the chromosome pair no. 1. Hybridization with telomeric probes (TTAGGG)n showed signals at the end of all chromosomes. 5S rDNA was cloned and sequenced. After the alignment, the 5S rRNA sequences revealed an organization made up of two different classes of tandem arrays (type I and type II). FISH with 5S rDNA marked the telomeric regions of the small chromosome pair no. 15, while FISH with 18S rDNA marked the telomeric region of the pair no. 1. The results obtained were compared with cariological data on closer species now available in literature.

Karyotypic characterization and genomic organization of the 5S rDNA in Polypterus senegalus (Osteichthyes, Polypteridae)

“…After BLAST/N searches, 5S rDNA type I in P. senegalus showed high similarity with 5S coding regions of different fish species. The same sequence showed a 93% identity with the coding region of 5S rDNA type II, in the same species, and an 85% identity with E. calabaricus 5S rDNA type I (Morescalchi et al 2006). The single monomeric unit of 5S type II is shorter (249 bp-GenBank accession number EF127898): it contains a 5S coding region of 122 bp with an internal ICR of 36 bp (position 65-100) and a successive NTS 1 region (position 123-249), containing a single microsatellite (CT) tandem repeats sequence (position 161-190).…”

“…If the morphological, developmental and molecular studies on the relationships of these species with other taxa are numerous, on the contrary scarce are data regarding the karyology of the Polypteridae family (Denton and Howell 1973;Capanna and Cataudella 1973;Urushido et al 1977;Cataudella et al 1978;Vervoort 1980a, b;Morescalchi 2005;Morescalchi et al 2001Morescalchi et al , 2006. To improve the knowledge on chromosomal structures and evolution in these species, we described the karyotype from twenty specimens of both sexes of P. senegalus, coming from Niger River.…”

Characterization of Japanese flounder karyotype by chromosome bandings and fluorescence in situ hybridization with DNA markers

“…Colocalization of 5S and 18S rDNA loci on chromosome 1 is an intriguing finding, since these loci were usually located on different chromosome pairs in fish (e.g., Inafuku et al 2000;Martins and Galetti 2001;Morescalchi et al 2006;Noleto et al 2006;Rosa et al 2006). Moreover, such colocalization has recently been interpreted as an ancestral condition of two classes of rDNA loci in fish genome (Fontana et al 2003).…”

Telomeres in Fishes

“…In fish, the chromosomal distribution of the telomeric DNA sequences is described in approximately 74 rayfinned species (Actinopterygii), 1 lobe-finned fish (Sarcopterygii) [Moreschalchi et al, 2002] and 4 cartilaginous fishes (Chondrichthyes) [Rocco et al, 2001. Among actinopterygians, chromosomal location of the telomeric DNA repeats has been examined in the Chondrostei species from 2 orders: Acipenseriformes [Fontana et al, 1998[Fontana et al, , 2004[Fontana et al, , 2008 and Polypteriformes [Moreschalchi et al, 2007[Moreschalchi et al, , 2008. Within ray-finned fish of the infraclass Teleostei, the chromosomal distribution of the telomeric DNA sequences has been studied in fish species belonging to 15 orders: Anguilliformes [Salvadori et al, 1995], Batrachoidoformes [Merlo et al, 2007], Characiformes [de Marco Ferro et al, 2003;, Cypriniformes [Meyne et al, 1990;Gornung et al, 1998;Sola et al, 2003a;Ocalewicz et al, 2004a;Gromicho et al, 2006;Schmid et al, 2006], Gasterosteiformes [Ocalewicz et al, 2011], Gymnotiformes [Milhomem et al, 2008;Silva et al, 2009;Felippe and Foresti, 2010;Scacchetti et al, 2011], Mugiliformes [Gornung et al, 2004;Rossi et al, 2005], Osmeriformes , Perciformes [Mandrioli et al, 2000;Sola et al, 2000Sola et al, , 2003bChew et al, 2002;Molina and Galetti, 2002;Mota-Velasco et al, 2010;Wang et al, 2010;Jacobina et al, 2011;Ocalewicz and Sapota, 2011;Jankun et al, 2013], Pleuronectiformes …”