Branchiostoma lanceolatum

Amphioxus is the most basal living representative of the evolutionary lineage of chordates. The adult anatomy of amphioxus is vertebrate-like, but simpler. They possess typical chordate characters such as a dorsal hollow neural tube and notochord, a ventral gut and a perforated pharynx with gill slits, segmented axial muscles and gonads, a post-anal tail, a pronephric kidney and homologues of the adenohypophysis and thyroid gland.

For all these reasons amphioxus is an invaluable animal model for understanding the invertebrate-chordate to vertebrate evolutionary transition. To do so, the study of embryonic development is essential, and the amphioxus species used in this project, Branchiostoma lanceolatum, is able to produce embryos on a daily basis during the spawning season, unlike other amphioxus species.
The amphioxus genome is often viewed as “archetypal” for the chordate lineage. The main reason is that amphioxus and vetebrates not only share a high morphological conservation but they also share genomic conservation, both at the gene content and genome structure levels. However, during the evolution of the vertebrate lineage two complete genome duplications occurred. Amphioxus diverged before these genome duplications, but the “preduplicated” amphioxus genome possesses almost all the gene families that presumably existed in the ancestor of chordates. The consequences of these duplications are that for each amphioxus gene a paralogy group of 1 to 4 genes can be found in mammalian genomes. Moreover, amphioxus is the only non-vertebrate organism where conservation of cis-regulatory elements in noncoding regions of the genome can be found.
For all these reasons, the complete genome sequence of B. lanceolatum, proposed in this project, will allow detailed studies on the evolution of the vertebrate lineage, and also will permit the deduction of what the genome of the ancestor of all chordates looked like.