The integrin α6 subunit pairs with both the β1 and β4 subunits to form specific cellular receptors for laminin. We studied the α6 spatiotemporal expression pattern by RT-PCR and immuno-fluorescence and the α6 role by blocking antibodies in the early chick embryo. Combined RT-PCR and immunocytochemistry showed the first α6 expression at stage XIII (late blastula). The α6 mRNA spliced variant α6A and α6B expression was developmentally regulated. α6 expression was intense in cells ingressing through the primitive streak and the migrating mesenchymal cells (stage HH3-4). α6 expression was initially high in the neurectoderm as it epithelializes to form the neural plate (HH4) and showed a transient, dynamic distribution in the nervous system during development. α6 expression was strong in pre-somitic mesoderm during its compaction and epithelialization but was restricted only to the myotome in mature somites. The paired cardiac primordia and their apposing pharyngeal endoderm expressed α6 intensely (HH10-11). In the developing heart, α6 expression was intense in dorsal mesocardium and myocardium and was also detected in the single walled endocardium (HH17). α6 expression was strong in the prospective retina, lens, cornea and the site of optic stalk constriction at the time these tissues interact and epithelialize before the optic cup stage. Inhibition of the α6 function by blocking antibodies impeded neural crest cell migration, provoked the severe structural disorganization of the anterior encephalic and cardiac basement membranes and inhibited the conversion of mesenchymal to epithelial structures and seemed to be essential for the proper formation of the embryonic and extraembryonic vasculature.
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