Fig. 1. Olfactory neuron projection in Drosophila and mouse. (A)In Drosophila, the Notch on-off code (red, Notch off; green, Notch on) is involved in coupling antennal neuron axonal projections with their odorant receptor expression. (B) In the mouse, the odorant receptor code is transformed into gene expression patterns that regulate axonal fasciculation via neuronal activity (red and green indicate different adhesion molecules). The X and Y labels next to the cell bodies indicate odorant receptor types. The diamonds indicate homophilic adhesions.