Screening of Visual Center Specific Marker Molecules by Monoclonal Antibody Technique

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To clarify the molecular background of the specific neuronal connection between retinal axons and visual centers, we undertook to screen target specific maker molecules by the monoclonal antibody producing technique. A monoclonal antibody A5 (MAb-A5) which was prepared against mechanically dissociated tectal cells of Xenopus tadpoles (at stages 51-53) bound to laminas 8 and 9 (the sites of optic nerve innervation) of the tectum and also other minor visual centers in the diencephalon and midbrain, but not to the retina, optic nerve or optic tract. The epitope of the MAb-A5 (A5 antigen) was a cell surface protein molecule approximately 140 K in molecular weight. The A5 antigen appeared in the tectum at first at stage 39 of development when tectal invasion by retinal axons was initiated. Besides the visual centers, the A5 antigen also appeared in very restricted regions in the medulla and spinal cord. When eyes were transplanted on the back of Xenopus embryos, retinal axons from the transplanted eye preferentially arrived at the A5 antigen-positive regions in the medulla and spinal cord. These findings suggest that the A5 antigen may be a marker molecule of optic nerve targets, and may play important roles in the preferential guiding or trapping of ingrowing retinal axons.