VISUAL PROJECTION MAP SPECIFIED BY TOPOGRAPHIC EXPRESSION OF TRANSCRIPTION FACTORS IN THE RETINA

TOPOGRAPHICAL maps of neuronal connectivity occur in various brain reg ions(1). In the visual system of birds, retinal ganglion-cell axons fr om the anterior retina connect to a posterior part of the optic tectum , and posterior retinal axons connect to the anterior part, thereby es tablishing a point-to-point projection map(2,3). The chemoaffinity the ory(4) predicts that the orderly retinotectal projection is generated by a topographical arrangement of molecules. We report here that me ha ve found several genes topographically expressed along the nasotempora l (anterior-posterior) axis in the embryonic chicken retina. Among the se, two transcriptional regulators, belonging to the winged-helix fami ly(5) are expressed in a mutually exclusive manner in either the nasal or temporal part of the retina, Misexpression of each factor causes m isprojection on the tectum along the rostrocaudal axis, showing that t opographical expression of these transcription factors controls format ion of the retinotectal map.