Identification of multiple integrin β1 homologs in zebrafish (Danio rerio)

Background: Integrins comprise a large family of α,β heterodimeric, transmembrane cell adhesion receptors that mediate diverse essential biological functions. Higher vertebrates possess a single β1 gene, and the β1 subunit associates with a large number of α 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 β1 integrin sequences and functions in this organism. Results: Using RT-PCR, complete coding sequences of zebrafish β1 paralogs were obtained from zebrafish embryos or adult tissues. The results show that zebrafish possess two β1 paralogs (β1-1 and β1-2) that have a high degree of identity to other vertebrate β1 subunits. In addition, a third, more divergent, β1 paralog is present (β1-3), which may have altered ligand-binding properties. Zebrafish also have other divergent β1-like transcripts, which are C-terminally truncated forms lacking the transmembrane and cytoplasmic domains. Together with β1-3 these truncated forms comprise a novel group of β1 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 β1-1 and β1-2 occurred after the divergence of the tetrapod and fish lineages, while a subsequent duplication of the ancestor of β1-2 may have given rise to β1-3 and an ancestral truncated paralog. A very recent tandem duplication of the truncated β1 paralogs appears to have taken place. The different zebrafish β1 paralogs have varied patterns of temporal expression during development. β1-1 and β1-2 are ubiquitously expressed in adult tissues, whereas the other β1 paralogs generally show more restricted patterns of expression. Conclusion: Zebrafish have a large set of integrin β1 paralogs. β1-1 and β1-2 may share the roles of the solitary β1 subunit found in other vertebrates, whereas β1-3 and the truncated β1 paralogs may have acquired novel functions. © 2006 Mould et al; licensee BioMed Central Ltd.