We have identified a Drosophila member of the deleted in colorectal cancer (DCC) gene family. The frazzled gene encodes transmembrane proteins that contain four immunoglobulin C2 type domains, six fibronectin type III repeats, and a cytoplasmic domain of 278 amino acids. Like vertebrate members of the DCC family, Frazzled is expressed on axons in the embryonic central nervous system and on motor axons in the periphery. Frazzled is also expressed on epidermis and gut epithelium. Null mutants in frazzled are defective in axon guidance in the central nervous system and in motor axon guidance and targeting in the periphery. The phenotypes strongly resemble those of a deletion of the two Drosophila Netrin genes. We have rescued the frazzled CNS and motor axon defects by expressing Frazzled specifically in neurons; expression in target tissues does not rescue the phenotype. These data, together with vertebrate studies showing binding of DCC to netrin, suggest that Frazzled may function in vivo as a receptor or component of a receptor mediating Netrin-dependent axon guidance.

Voltage-dependent potassium, sodium and calcium ion channels may share a common mechanism of activation, in which the conserved S4 sequence acts as the primary voltage sensor. Site-directed mutagenesis of the S4 sequence of the Shaker potassium channel and electrophysiological analysis suggest that voltage-dependent activation involves the S4 sequence but is not solely due to electrostatic interactions.

The Shaker gene of Drosophila melanogaster encodes a potassium-selective ion channel, the 'A' channel, or one of its subunits. A single Shaker messenger RNA species suffices to direct the synthesis of functional A channels in Xenopus oocytes. Physiological characteristics of the A currents induced by two different mRNA species are compared.