RESTRICTED EXPRESSION OF THE IRREC-RST PROTEIN IS REQUIRED FOR NORMALAXONAL PROJECTIONS OF COLUMNAR VISUAL NEURONS

The 104 kDa irreC-rst protein, a member of the immunoglobulin superfam ily, mediates hemophilic adhesion in cell cultures. In larval optic ch iasms, the protein is found on recently formed axon bundles, not on ol der ones. In developing visual neuropils, it is present in all columna r domains of specific layers. The number of irreC-rst-positive neuropi l stratifications increases until the midpupal stage. Immunoreactivity fades thereafter. the functional importance of the restricted express ion pattern is demonstrated by the severe projection errors of axons i n the first and second optic chiasms in loss of function mutants and i n transformants that express the irreC-rst protein globally. Epigenesi s of the phenotypes can be explained partially on the bases of hemophi lic irreC-rst interactions.