Segade F, Cota C, Famiglietti A, Cha A, Davidson B.

Evodevo. 2016 Aug 31;7(1):21. doi: 10.1186/s13227-016-0056-4. eCollection 2016.

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.

See http://www.ncbi.nlm.nih.gov/pubmed/27583126

Figure 1: Comparison of the domain architecture of vertebrate and tunicate FN proteins. Protein domains in full-length Ciona intestinalis FN (3698 amino acids), human FN isoform 1 (accession number NP_001293061; 2477 amino acids) and lamprey (Petromyzon) FN (PMZ_0026015 [19]; fragment, 2457 amino acids) were identified with the SMART 7 domain prediction tool. FN and IG (immunoglobulin) domains as indicated in legend; red box signal peptide sequence; IIICS: type III connecting segment. Potential integrin-binding motifs (including IGD, NGR, KLDAP, DGR, LDV or RGD) and dimerization signal CxxxC are shown above the sequences