title: Fibronectin contributes to notochord intercalation in the invertebrate chordate, Ciona intestinalis.
abstract: BACKGROUND
  Genomic analysis has upended chordate phylogeny, placing the tunicates as the sister group to the vertebrates. This taxonomic rearrangement raises questions about the emergence of a tunicate/vertebrate ancestor.
  
  
  RESULTS
  Characterization of developmental genes uniquely shared by tunicates and vertebrates is one promising approach for deciphering developmental shifts underlying acquisition of novel, ancestral traits. The matrix glycoprotein Fibronectin (FN) has long been considered a vertebrate-specific gene, playing a major instructive role in vertebrate embryonic development. However, the recent computational prediction of an orthologous "vertebrate-like" Fn gene in the genome of a tunicate, Ciona savignyi, challenges this viewpoint suggesting that Fn may have arisen in the shared tunicate/vertebrate ancestor. Here we verify the presence of a tunicate Fn ortholog. Transgenic reporter analysis was used to characterize a Ciona Fn enhancer driving expression in the notochord. Targeted knockdown in the notochord lineage indicates that FN is required for proper convergent extension.
  
  
  CONCLUSIONS
  These findings suggest that acquisition of Fn was associated with altered notochord morphogenesis in the vertebrate/tunicate ancestor.
authors: Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104 USA.
authors: Fernando
authors: F
authors: Segade
authors: Department of Biology, Swarthmore College, 500 College Ave., Swarthmore, PA 19081 USA.
authors: Christina
authors: C
authors: Cota
authors: Section on Biological Chemistry, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892 USA.
authors: Amber
authors: A
authors: Famiglietti
authors: Department of Systems Biology, Harvard Medical School, Boston, MA USA.
authors: Anna
authors: A
authors: Cha
authors: Department of Biology, Swarthmore College, 500 College Ave., Swarthmore, PA 19081 USA.
authors: Brad
authors: 0000-0001-5082-7872
authors: B
authors: Davidson
keywords: Chordate evolution; Convergent extension; Extracellular matrix; Fibronectin; Notochord; Tunicates