Hering_2000_J.Comp.Neurol_424_153

The distribution of the beta1 integrin subunit was investigated in the developing and adult chick retina at the light and electron microscopic levels, using two different monoclonal antibodies. Western blotting revealed a single band with a molecular weight of approximately 130 kDa in the retina and in a number of other tissues, indicating the specificity of the antibodies. In the retina, immunoreactivity was detected on radial cells spanning the entire width between the pigment epithelium and the vitreal border. These cells were undifferentiated neuroepithelial cells at early stages and radial Muller glial cells at later stages of development. At all stages, the beta1 subunit was concentrated at the vitreal border of the retina around the inner limiting membrane. Mechanical isolation of the inner limiting membrane, as well as immunoelectron microscopy, demonstrated that this immunoreactivity was due to a concentration of the beta1 subunit in the endfeet of neuroepithelial and Muller glial cells. Injection of collagenase into the vitreous of live embryos, a procedure that selectively removes the inner limiting membrane, but does not proteolytically degrade the integrin protein, resulted in a redistribution of the integrin immunoreactivity, demonstrating that the integrity of the basal lamina is required for the maintenance of the concentration of the beta1 subunit in the endfeet. These results suggest a role for the beta1 subunit-containing integrin heterodimers in the adhesion of neuroepithelial and Muller glial cells to extracellular matrix components of the inner limiting membrane, possibly stabilizing the radial morphology of these cells.