Distribution of the integrin beta 1 subunit on radial cells in the embryonic and adult avian retina

The distribution of the beta 1 integrin subunit was investigated in the dev eloping and adult chick retina at the light and electron microscopic levels , using two different monoclonal antibodies. Western blotting revealed a si ngle band with a molecular weight of approximately 130 kDa in the retina an d in a number of other tissues, indicating the specificity of the antibodie s. In the retina, immunoreactivity was detected on radial cells spanning th e entire width between the pigment epithelium and the vitreal border. These cells were undifferentiated neuroepithelial cells at early stages and radi al Muller glial cells at later stages of development. At all stages, the be ta 1 subunit was concentrated at the vitreal border of the retina around th e inner limiting membrane. Mechanical isolation of the inner limiting membr ane, as well as immunoelectron microscopy, demonstrated that this immunorea ctivity was due to a concentration of the beta 1 subunit in the endfeet of neuroepithelial and Muller glial cells. Injection of collagenase into the v itreous of live embryos, a procedure that selectively removes the inner Lim iting membrane, but does not proteolytically degrade the integrin protein, resulted in a redistribution of the integrin immunoreactivity, demonstratin g that the integrity of the basal lamina is required for the maintenance of the concentration of the beta 1 subunit in the endfeet. These results sugg est a role for the beta 1 subunit-containing integrin heterodimers in the a dhesion of neuroepithelial and Muller glial cells to extracellular matrix c omponents of the inner limiting membrane, possibly stabilizing the radial m orphology of these cells. J. Comp. Neurol. 424:153-164, 2000. (C) 2000 Wile y-Liss, Inc.