Chromosomal mapping of the major and minor ribosomal genes, (GATA) n and (TTAGGG) n by one-color and double-color FISH in the toadfish Halobatrachus didactylus (Teleostei: Batrachoididae)

Abstract

The karyotype of Halobatrachus didactylus presents 46 chromosomes, composed of eight metacentric, 18 submetacentric, four subtelocentric, and 16 acrocentric chromosomes. The results of FISH showed that the major ribosomal genes were located in the terminal position of the short arm of a large submetacentric chromosome. They also showed a high variation in the hybridization signals. The products of amplification of 5S rDNA produced bands of about 420 pb. The PCR labeled products showed hybridization signals in the subcentromeric position of the long arm of a submetacentric chromosome of medium size. Double-color FISH indicated that the two ribosomal families are not co-located since they hybridized in different chromosomal pairs. Telomeres of all the chromosomes hybridized with the (TTAGGG)n probe. The GATA probe displayed a strong signal in the long arm of a submetacentric chromosome of medium size, in the subcentromeric position. The double-color FISH showed that the microsatellite GATA and the 5S rDNA gene are located in different chromosomal pairs. The majority presence of GATA probes in one pair of chromosomes is unusual and considering its distribution through different taxa it could be due to evolutionary mechanisms of heterochromatine accumulation, leading to the formation of differentiated sex chromosomes.

Karyoevolution of the toadfish Thalassophryne nattereri (Batrachoidiformes: Batrachoididae)

“…This result agrees with the pattern reported in several toadfish species (Palazón et al, 2003;Nirchio et al, 2004a,b;Merlo et al, 2007), thus suggesting that single NORs at the telomeric position should be regarded as a symplesiomorphic feature of Batrachoididae. The localization of ribosomal sites in distinct chromosome pairs could validate these regions as potential tools for cytotaxonomic purposes.…”

“…Fluorescence in situ hybridization analyses in the same species using telomeric and (GATA)n probes failed to locate ectopic telomeric sites, while the GATA repeats were detected at the interstitial position on a single chromosome pair (Merlo et al, 2007). The absence of internal telomere-like sequences could be related either to the exclusion of these sites during fusion events or to the long time period since the numerical reduction in relation to the primitive teleostean karyotype (2n = 48 to 2n = 44-46) took place in Batrachoididae.…”

“…Contradictory karyotypic formulae have been reported in a single species of Batrachoididae (Palazón et al, 2003;Merlo et al, 2007), and some of them are quite discrepant (Nirchio et al, 2002(Nirchio et al, , 2004a. However, the relatively large number of subtelocentric chromosomes in the karyotypes coupled with an imprecise differentiation between subtelocentric and acrocentric chromosomes should account for most of the differences in the number of chromosome arms observed within this family.…”

Analysis of three multigene families as useful tools in species characterization of two closely-related species, Dicentrarchus labrax, Dicentrarchus punctatus and their hybrids

“…Labeling of probes was performed by PCR-based method using the primer sets 1, 3 and 4, for 5S rDNA, 18S rDNA and U2 snRNA respectively. Cycles and PCR conditions, as well as conditions of hybridization and post-hybridization washes, were according to Cross et al (2003) and Merlo et al (2007).…”

Cloning and characterization of Vasa gene expression pattern in adults of the Lusitanian toadfish Halobatrachus didactylus

“…In addition, different aspects of reproduction have been studied in H. didactylus (Palazón-Fernández et al 2001, Modesto & Canário 2003. Recently, cytogenetic and molecular studies have been carried out (Merlo et al 2007, Úbeda-Manzanaro et al 2014 in Batrachoididae fish species, which are considered one of the most highly evolved groups of marine teleosts (Modesto & Canário 2003).…”