title: Molecular evolution of SPARC: absence of the acidic module and expression in the endoderm of the starlet sea anemone, Nematostella vectensis.
abstract: The matricellular glycoprotein SPARC is composed of three functional domains that are evolutionarily conserved in organisms ranging from nematodes to mammals: a Ca(2+)-binding glutamic acid-rich acidic domain at the N-terminus (domain I), a follistatin-like module (domain II), and an extracellular Ca(2+)-binding (EC) module that contains two EF-hands and two collagen-binding epitopes (domain III). We report that four SPARC orthologs (designated nvSPARC1-4) are expressed by the genome of the starlet anemone Nematostella vectensis, a diploblastic basal cnidarian composed of an ectoderm and endoderm separated by collagen-based mesoglea. We also report that domain I is absent from all N. vectensis SPARC orthologs. In situ hybridization data indicate that N. vectensis SPARC mRNAs are restricted to the endoderm during post-gastrula development. The absence of the Ca(2+)-binding N-terminal domain in cnidarians and conservation of collagen-binding epitopes suggests that SPARC first evolved as a collagen-binding matricellular glycoprotein, an interaction likely to be dependent on the binding of Ca(2+)-ions to the two EF-hands in the EC domain. We propose that further Ca(2+)-dependent activities emerged with the acquisition of an acidic N-terminal module in triplobastic organisms.
authors.affiliation: Laboratory of Tissue Repair and Regeneration, Matrix Dynamics Group, University of Toronto, 150 College Street, Toronto, ON, Canada.
authors.forename: Anne
authors.initials: A
authors.lastname: Koehler
authors.forename: Sherwin
authors.initials: S
authors.lastname: Desser
authors.forename: Belinda
authors.initials: B
authors.lastname: Chang
authors.forename: Jacqueline
authors.initials: J
authors.lastname: MacDonald
authors.forename: Ulrich
authors.initials: U
authors.lastname: Tepass
authors.forename: Maurice
authors.initials: M
authors.lastname: Ringuette
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D015676:Osteonectin / Q000737:chemistry / Q000235:genetics*; D017434:Protein Structure, Tertiary; D012615:Sea Anemones / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D015676:Osteonectin