Integrating cytogenetics and genomics in comparative evolutionary studies of cichlid fish.

Background: The availability of a large number of recently sequenced vertebrate genomes opens new avenues to integrate cytogenetics and genomics in comparative and evolutionary studies. Cytogenetic mapping can offer alternative means to identify conserved synteny shared by distinct genomes and also to define genome regions that are still not fine characterized even after wide-ranging nucleotide sequence efforts. An efficient way to perform comparative cytogenetic mapping is based on BAC clones mapping by fluorescence in situ hybridization.

Genomic content and new insights on the origin of the B chromosome of the cichlid fish Astatotilapia latifasciata.

B chromosomes are additional chromosomes widely studied in a diversity of eukaryotic groups, including fungi, plants and animals, but their origin, evolution and possible functions are not clearly understood. To further understand the genomic content and the evolutionary history of B chromosomes, classical and molecular cytogenetic analyses were conducted in the cichlid fish Astatotilapia latifasciata, which harbor 1–2 B chromosomes. Through cytogenetic mapping of several probes, including transposable elements, rRNA genes, a repeated DNA genomic fraction (C0t - 1 DNA), whole genome probes (comparative genomic hybridization), and BAC clones from Oreochromis niloticus, we found similarities between the B chromosome and the 1st chromosome pair and chromosomes harboring rRNA genes.

Comparative cytogenetic mapping of Sox2 and Sox14 in cichlid fishes and inferences on the genomic organization of both genes in vertebrates.

To better understand the genomic organization and evolution of Sox genes in vertebrates, we cytogenetically mapped Sox2 and Sox14 genes in cichlid fishes and performed comparative analyses of their orthologs in several vertebrate species. The genomic regions neighboring Sox2 and Sox14 have been conserved during vertebrate diversification. Although cichlids seem to have undergone high rates of genomic rearrangements, Sox2 and Sox14 are linked in the same chromosome in the Etroplinae Etroplus maculatus that represents the sister group of all remaining cichlids.

Cytogenetic mapping of the retroelements Rex1, Rex3 and Rex6 among cichlid fish: new insights on the chromosomal distribution of transposable elements.

To enhance our understanding of the organization of the genome and chromosome evolution of cichlid fish species, we have isolated and physically mapped onto the chromosomes the transposable elements (TEs) Rex1, Rex3 and Rex6, which are conserved in teleost fish, in the chromosomes of African and South American cichlid species. The physical mapping of different Rex elements showed that they are primarily compartmentalized in the pericentromeric heterochromatic regions, although dispersed or clustered signals in euchromatic regions were also observed. The presence of TEs in heterochromatin can be correlated with their role in the structure and organization of heterochromatic areas (such as centromeres) or with the lower selective pressure that act on these gene-poor regions.