CHARACTERIZATION OF THE INTEGRIN ALPHA-8 SUBUNIT - A NEW INTEGRIN BETA-1-ASSOCIATED SUBUNIT, WHICH IS PROMINENTLY EXPRESSED ON AXONS AND ON CELLS IN CONTACT WITH BASAL LAMINAE IN CHICK-EMBRYOS

In this article, we describe the primary structure, the biochemical characterization and the tissue distribution of a novel integrin alpha-subunit, named alpha-8. This subunit associates with the integrin-beta-1 subunit to form alpha-8-beta-1 heterodimers. By sequence analysis, alpha-8 is more closely related to the alpha-5 and alpha-v subunits than to other characterized integrin-alpha-subunits, but is clearly distinct from each of these. The alpha-8 subunit is expressed at moderate levels in several epithelial cells where its localization adjacent to basal laminae suggests that alpha-8-containing heterodimers interact with at least one extracellular matrix constituent. In embryos, the highest levels of alpha-8 protein expression are seen in the nervous system where alpha-8 is strongly expressed by several classes of projection neurons. The alpha-8 subunit is concentrated in axon tracts, including major projections in the spinal cord, optic system and auditory system. This tissue specific expression and cellular localization suggest that alpha-8-containing integrin receptors might promote axon outgrowth in the embryonic nervous system.