Molecular Cytogenetic Analysis of the European Hake Merluccius merluccius (Merlucciidae, Gadiformes): U1 and U2 snRNA Gene Clusters Map to the Same Location

Abstract

The European hake (Merluccius merluccius) is a highly valuable and intensely fished species in which a long-term alive stock has been established in captivity for aquaculture purposes. Due to their huge economic importance, genetic studies on hakes were mostly focused on phylogenetic and phylogeographic aspects; however chromosome numbers are still not described for any of the fifteen species in the genus Merluccius. In this work we report a chromosome number of 2n = 42 and a karyotype composed of three meta/submetacentric and 18 subtelo/telocentric chromosome pairs. Telomeric sequences appear exclusively at both ends of every single chromosome. Concerning rRNA genes, this species show a single 45S rDNA cluster at an intercalary location on the long arm of subtelocentric chromosome pair 12; the single 5S rDNA cluster is also intercalary to the long arm of chromosome pair 4. While U2 snRNA gene clusters map to a single subcentromeric position on chromosome pair 13, U1 snRNA gene clusters seem to appear on almost all chromosome pairs, but showing bigger clusters on pairs 5, 13, 16, 17 and 19. The brightest signals on pair 13 are coincident with the single U2 snRNA gene cluster signals. Therefore, the use of these probes allows the unequivocal identification of at least 7 of the chromosome pairs that compose the karyotype of Merluccius merluccius thus opening the way to integrate molecular genetics and cytological data on the study of the genome of this important species.

Cytogenetic analysis of the genus Thoropa Cope, 1865 (Anura-Cycloramphidae) with evolutionary inferences based on repetitive sequences

“…The marking in pair 6 is repeated for all the species and populations, except for T. saxatilis; however, in the T. miliaris population of Santa Teresa, ES,, and in the two populations of T. taophora (Ubatuba and São Sebastião, SP), the marking occurs at the end (telomeric region) of the short arm of pair 6, indicating a possible inversion in the population of Paraty, RJ. Despite having highly conserved sequences in eukaryotes, snDNA U2 vary in number and organization in the genomes of different species (Úbeda-Manzanaro et al, 2010;Garcia-Souto et al, 2015).…”

Characterization of a male specific region containing a candidate sex determining gene in Atlantic cod

“…This could partly be solved by production of all-female triploid stocks 4,31,32 . Gynogenetic and sex-reversed cod populations have demonstrated a XX-XY sex determination system 21,33,34 , but karyotyping of Atlantic cod and the closely related European hake ( Merluccius merluccius ) failed to reveal sex-linked chromosome heteromorphism 35,36 . Recently, whole genome sequence data from wild Atlantic cod was used to identify genotypes segregating closely with a XX-XY system in six putative sex determining regions distributed across five linkage groups 37 .…”

Molecular Analysis and Chromosome Mapping of Repetitive DNAs in the Green TerrorAndinoacara rivulatus(Cichlidae: Cichlasomatini)

“…62 Indeed, these genes usually show high variability at molecular level, as they are associated with other genes, microsatellites or transposable elements, and low variability at chromosomal level. 88 Regarding U1 snRNA, chromosomal localization of coding genes has been investigated so far only in a few teleost fishes of the family Hepsetidae, 16 Mugilidae, 20 Merlucciidae, 90 and Characidae, 50 and in the latter they are often associated with 5S ribosomal genes. In Cichlidae, 91 mapping of the U1 snRNA in 19 species belonging to different subfamilies had shown positive signals located on a single chromosome pair, mainly (14 out of 19 species) terminally on the long arms.…”