Expression of α4 Integrin mRNA and Protein and Fibronectin in the Early Chicken Embryo

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Abstract
α4 integrins (α4β1 and α4β7) have been shown to mediate both cell-matrix adhesion to fibronectin and cell-cell adhesion to VCAM-1. These interactions have been suggested to contribute to hematopoiesis, lymphocyte homing, recruitment of inflammatory cells, neural crest cell migration and myogenesis. We report here the cloning of chicken α4 cDNA and its use to define the patterns of expression of α4 mRNA and protein in early chicken embryos (19–22 somite pairs), a stage at which neural crest cells can be examined at various points in their migration and somitic development and differentiation can also be observed at various stages. We observe widespread expression of both α4 mRNA and protein, although the patterns of steady state expression do not conform precisely. Many neural crest cells contain significant levels of α4 mRNA. Some neural crest cells express α4 protein but its expression is transient and/or limited to a subset of these cells. α4 is strongly expressed at both mRNA and protein levels by somitic cells and their derivatives in the sclerotome, dermatome and myotome and is also expressed in neural tube, otic placode, heart, gut endoderm and some other tissues. Comparison with the distributions of fibronectin shows that, although some α4 expression occurs in locations consistent with a role in cell-matrix adhesion to fibronectin, α4 is also expressed in other places where fibronectin is low or absent and a role for α4 in cell-cell interactions appears more likely.