Target-independent regulation of a novel growth associated protein in the visual system of the chicken

Using an immunosuppression technique, the monoclonal antibody 2A1 has been generated specific for a 140 x 10(3) Mr cytoplasmic-membrane-associated protein as shown by subcellular fractionation and Western blot analysis. The antigen is initially confined to perikarya of postmitotic migratory ganglion cells of the embryonic chick retina as revealed by bromodeoxyuridine labeling. During the subsequent period of axon outgrowth, the antigen becomes restricted to ganglion cell axons but disappears during the innervation of the tectum opticum, suggesting a tectal inhibition of antigen expression in retinal axons. To analyse whether the tectum suppresses 2A1-antigen expression, optic nerves of chick embryos were severed to prevent tectal innervation. 2A1-immunoreactivity was determined in deflected axons in comparison to control axons. In addition, retinal axons were grown in vitro on a substratum consisting of alternating stripes of laminin and tectal membranes, in order to investigate whether retinal axons become devoid of the 2A1-antigen once they cross from laminin to tectal membranes. However, neither prevention of target innervation by optic nerve transection in vivo nor exposure of retinal axons to soluble or particulate tectal components in vitro modify 2A1-antigen regulation in ganglion cell axons, suggesting a retina inherent-control of gene expression. Antigen expression is essentially restricted to the period of axonal outgrowth and therefore the 2A1-protein is likely to be involved in processes essential for neurite extension, independent of the synaptic target.