The Draft Genome of <i>Ciona intestinalis</i> : Insights into Chordate and Vertebrate Origins

TLDR

The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago, and the modern ascidian tadpole represents a plausible approximation to these ancestral chordates. The study aims to illuminate the origins of chordate and vertebrates by sequencing the protein‑coding genome of the ascidian *Ciona intestinalis*. The authors generated a draft of the protein‑coding portion of the *Ciona intestinalis* genome. The draft genome contains ~16,000 protein‑coding genes—about half the number in vertebrates—and shows that vertebrate gene families are simplified in *Ciona*, while lineage‑specific innovations such as cellulose‑metabolism genes related to bacteria and fungi have been acquired.

Abstract

The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis . The Ciona genome contains ∼16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona , suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.