Developmental loss of functional laminin receptors on retinal ganglion cells is regulated by their target tissue, the optic tectum

The ability of chick retinal ganglion cells (RGCs) to extend neurites on tissue culture substrata of the extra-cellular matrix protein laminin is lost during embryonic development. In order to establish the mechanism responsible for the loss of response, the number of high affinity (KD 10(-9) M) laminin receptors on both the cell bodies and neurites of RGCs were determined throughout this period by a ligand binding assay using radio-labelled laminin. It was found that the loss of response paralleled a decrease in receptor numbers on both the cell bodies and the neurites of the RGCs. Bilateral tectal ablation at embryonic day 6 resulted in the subsequent maintenance of laminin-stimulated neurite outgrowth, together with a partial inhibition of the loss of laminin receptors. Thus, the loss of response of the RGCs to laminin reflects a decrease in the numbers of laminin receptors on these neurons, and furthermore, this down-regulation is in turn dependent on innervation of the target tissue.