We describe two male-specific olfactory receptors (ORs) in the silk moth, Bombyx mori, that are mutually exclusively expressed in a pair of adjacent pheromone-sensitive neurons of male antennae: One is specifically tuned to bombykol, the sex pheromone, and the other to bombykal, its oxidized form. Both pheromone ORs are coexpressed with an OR from the highly conserved insect OR subfamily. This coexpression promotes the functional expression of pheromone receptors and confers ligand-stimulated nonselective cation channel activity. The same effects were also observed for general ORs. Both odorant and pheromone signaling pathways are mediated by means of a common mechanism in insects.

In animals with binocular vision, retinal ganglion cell (RGC) axons either cross or avoid the midline at the optic chiasm. Here, we show that ephrin-Bs in the chiasm region direct the divergence of retinal axons through the selective repulsion of a subset of RGCs that express EphB1. Ephrin-B2 is expressed at the mouse chiasm midline as the ipsilateral projection is generated and is selectively inhibitory to axons from ventrotemporal (VT) retina, where ipsilaterally projecting RGCs reside. Moreover, blocking ephrin-B2 function in vitro rescues the inhibitory effect of chiasm cells and eliminates the ipsilateral projection in the semiintact mouse visual system. A receptor for ephrin-B2, EphB1, is found exclusively in regions of retina that give rise to the ipsilateral projection. EphB1 null mice exhibit a dramatically reduced ipsilateral projection, suggesting that this receptor contributes to the formation of the ipsilateral retinal projection, most likely through its repulsive interaction with ephrin-B2.

Sex pheromones released by female moths are detected with high specificity and sensitivity in the olfactory sensilla of antennae of conspecific males. Bombykol in the silkmoth Bombyx mori was the first sex pheromone to be identified. Here we identify a malespecific G protein-coupled olfactory receptor gene, B. mori olfactory receptor 1 (BmOR-1), that appears to encode a bombykol receptor. The BmOR-1 gene is located on the Z sex chromosome, has an eight-exon͞seven-intron structure, and exhibits malespecific expression in the pheromone receptor neurons of male moth antenna during late pupal and adult stages. Bombykol stimulation of Xenopus laevis oocytes expressing BmOR-1 and BmG␣q elicited robust dose-dependent inward currents on twoelectrode voltage clamp recordings, demonstrating that the binding of bombykol to BmOR-1 leads to the activation of a BmG␣q-mediated signaling cascade. Antennae of female moths infected with BmOR-1-recombinant baculovirus showed electrophysiological responses to bombykol but not to bombykal. These results provide evidence that BmOR-1 is a G protein-coupled sex pheromone receptor that recognizes bombykol.baculovirus ͉ bombykal ͉ bombykol ͉ olfactory receptor ͉ Xenopus laevis oocyte