Complete HOX cluster characterization of the coelacanth provides further evidence for slow evolution of its genome.

The living coelacanth is a lobe-finned fish that represents an early evolutionary departure from the lineage that led to land vertebrates, and is of extreme interest scientifically. It has changed very little in appearance from fossilized coelacanths of the Cretaceous (150 to 65 million years ago), and is often referred to as a "living fossil." An important general question is whether long-term stasis in morphological evolution is associated with stasis in genome evolution. To this end we have used targeted genome sequencing for acquiring 1,612,752 bp of high quality finished sequence encompassing the four HOX clusters of the Indonesian coelacanth Latimeria menadoensis. Detailed analyses were carried out on genomic structure, gene and repeat contents, conserved noncoding regions, and relative rates of sequence evolution in both coding and noncoding tracts. Our results demonstrate conclusively that the coelacanth HOX clusters are evolving comparatively slowly and that this taxon should serve as a viable outgroup for interpretation of the genomes of tetrapod species.

Genome enablement of the notothenioidei: genome size estimates from 11 species and BAC libraries from 2 representative taxa.

The perciform suborder Notothenoidei provides a compelling opportunity to study the adaptive radiation of a marine species flock in the cold Southern Ocean surrounding Antarctica. To enable genome-level studies of these psychrophilic fishes, we estimated the sizes of the genomes of 11 Antarctic species and generated high-quality BAC libraries for 2, the notothen Notothenia coriiceps and the icefish Chaenocephalus aceratus. Our results indicate that evolution of phylogenetically derived notothenioid families, [e.g., the icefishes (Channichthyidae)], was accompanied by genome expansion. Species (n=6) of the basal family Nototheniidae had C values that ranged between 0.98 and 1.20 pg, whereas those of the icefishes, the notothenioid crown group, were 1.66-1.83 pg (n=4 species). The BAC libraries VMRC-19 (N. coriiceps) and VMRC-21 (C. aceratus) comprised 12X and 10X coverage of the respective genomes and had average insert sizes of 138 and 168 kb. Greater than 60% of paired BAC ends sampled from each library ( approximately 0.1% of each genome) contained repetitive sequences, and the repetitive element landscapes of the 2 genomes (13.4% of the N. coriiceps genome and 14.5% for C. aceratus) were similar. The representation and depth of coverage of the libraries were verified by identification of multiple Hox gene contigs: six discrete Hox clusters were found in N. coriiceps and at least five Hox clusters were found in C. aceratus. Given the unusual anatomical and physiological adaptations of the notothenioids, the availability of these BAC libraries sets the stage for expanded analysis of the psychrophilic mode of life.