Unexpected diversity of cnidarian integrins: expression during coral gastrulation.
BACKGROUND
Adhesion mediated through the integrin family of cell surface receptors is central to early development throughout the Metazoa, playing key roles in cell-extra cellular matrix adhesion and modulation of cadherin activity during the convergence and extension movements of gastrulation. It has been suggested that Caenorhabditis elegans, which has a single beta and two alpha integrins, might reflect the ancestral integrin complement. Investigation of the integrin repertoire of anthozoan cnidarians such as the coral Acropora millepora is required to test this hypothesis and may provide insights into the original roles of these molecules.


RESULTS
Two novel integrins were identified in Acropora. AmItgalpha1 shows features characteristic of alpha integrins lacking an I-domain, but phylogenetic analysis gives no clear indication of its likely binding specificity. AmItgbeta2 lacks consensus cysteine residues at positions 8 and 9, but is otherwise a typical beta integrin. In situ hybridization revealed that AmItgalpha1, AmItgbeta1, and AmItgbeta2 are expressed in the presumptive endoderm during gastrulation. A second anthozoan, the sea anemone Nematostella vectensis, has at least four beta integrins, two resembling AmItgbeta1 and two like AmItgbeta2, and at least three alpha integrins, based on its genomic sequence.


CONCLUSIONS
In two respects, the cnidarian data do not fit expectations. First, the cnidarian integrin repertoire is more complex than predicted: at least two betas in Acropora, and at least three alphas and four betas in Nematostella. Second, whereas the bilaterian alphas resolve into well-supported groups corresponding to those specific for RGD-containing or laminin-type ligands, the known cnidarian alphas are distinct from these. During early development in Acropora, the expression patterns of the three known integrins parallel those of amphibian and echinoderm integrins.
Knack
Brent A
BA
ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia. brent.knack@jcu.edu.au
Iguchi
Akira
A
Shinzato
Chuya
C
Hayward
David C
DC
Ball
Eldon E
EE
Miller
David J
DJ
D000595:Amino Acid Sequence; D000818:Animals; D037421:Anthozoa / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D002448:Cell Adhesion; D054262:Gastrulation / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D014644:Genetic Variation; D017403:In Situ Hybridization; D039001:Integrin alpha Chains / Q000096:biosynthesis*; D039641:Integrin beta Chains / Q000096:biosynthesis*; D016013:Likelihood Functions; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment
D039001:Integrin alpha Chains; D039641:Integrin beta Chains