Elephant shark genome
Cartilaginous fishes (Chondrichthyes) are the phylogenetically oldest group of living jawed vertebrates (gnathostomes) and thus constitute an important group for understanding the origin of complex developmental and physiological systems in jawed vertebrates. They are also a useful outgroup to bony vertebrates (comprising ray-finned fishes, lobe-finned fishes and tetrapods) and can help in identifying specialized features that have led to the evolution of diverse groups of bony vertebrates. Cartilaginous fishes differ from bony vertebrates mainly by possessing a largely cartilaginous endoskeleton and lacking bone. There are about 1,000 species of cartilaginous fishes that are divided into two broad groups: the holocephalans (chimaeras) and elasmobranchs (sharks, rays and skates). We proposed elephant shark (Callorhinchus milii), a holocephalan, as a model cartilaginous fish genome because of its smallest genome (~1 Gb) among known cartilaginous fishes. Survey sequencing (1.4× coverage Sanger sequences; accession number AAVX01000000) indicated that unlike teleost fishes, the elephant shark has not experienced an additional round of whole genome duplication, underscoring its importance as a useful reference genome. We have now obtained a whole-genome assembly of the elephant shark using a combination of next-generation and Sanger sequencing. The annotated genome assembly and other resources are presented here.