Identification of multiple integrin beta1 homologs in zebrafish (Danio rerio).
BACKGROUND
Integrins comprise a large family of alpha,beta heterodimeric, transmembrane cell adhesion receptors that mediate diverse essential biological functions. Higher vertebrates possess a single beta1 gene, and the beta1 subunit associates with a large number of alpha subunits to form the major class of extracellular matrix (ECM) receptors. Despite the fact that the zebrafish (Danio rerio) is a rapidly emerging model organism of choice for developmental biology and for models of human disease, little is currently known about beta1 integrin sequences and functions in this organism.


RESULTS
Using RT-PCR, complete coding sequences of zebrafish beta1 paralogs were obtained from zebrafish embryos or adult tissues. The results show that zebrafish possess two beta1 paralogs (beta1-1 and beta1-2) that have a high degree of identity to other vertebrate beta1 subunits. In addition, a third, more divergent, beta1 paralog is present (beta1-3), which may have altered ligand-binding properties. Zebrafish also have other divergent beta1-like transcripts, which are C-terminally truncated forms lacking the transmembrane and cytoplasmic domains. Together with beta1-3 these truncated forms comprise a novel group of beta1 paralogs, all of which have a mutation in the ADMIDAS cation-binding site. Phylogenetic and genomic analyses indicate that the duplication that gave rise to beta1-1 and beta1-2 occurred after the divergence of the tetrapod and fish lineages, while a subsequent duplication of the ancestor of beta1-2 may have given rise to beta1-3 and an ancestral truncated paralog. A very recent tandem duplication of the truncated beta1 paralogs appears to have taken place. The different zebrafish beta1 paralogs have varied patterns of temporal expression during development. Beta1-1 and beta1-2 are ubiquitously expressed in adult tissues, whereas the other beta1 paralogs generally show more restricted patterns of expression.


CONCLUSIONS
Zebrafish have a large set of integrin beta1 paralogs. beta1-1 and beta1-2 may share the roles of the solitary beta1 subunit found in other vertebrates, whereas beta1-3 and the truncated beta1 paralogs may have acquired novel functions.
Mould
A Paul
AP
Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK. paul.mould@manchester.ac.uk
McLeish
Jennifer A
JA
Huxley-Jones
Julie
J
Goonesinghe
Alexander C
AC
Hurlstone
Adam F L
AF
Boot-Handford
Raymond P
RP
Humphries
Martin J
MJ
D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D019012:Integrin beta1 / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D009928:Organ Specificity; D010802:Phylogeny; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D017434:Protein Structure, Tertiary; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014714:Vertebrates / Q000235:genetics; D015027:Zebrafish / Q000196:embryology / Q000235:genetics* / Q000254:growth & development; D029961:Zebrafish Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology
D019012:Integrin beta1; D020033:Protein Isoforms; D029961:Zebrafish Proteins