THE DROSOPHILA 18-WHEELER IS REQUIRED FOR MORPHOGENESIS AND HAS STRIKING SIMILARITIES TO TOLL

We have isolated and characterized a novel gene, named 18 wheeler (18w ) for its unique segmental expression pattern in Drosophila embryos an d expression incells that migrate extensively. 18,wheeler transcripts accumulate in embryos in a pattern reminiscent of segment polarity gen es. Mutations in 18w cause death during larval development and early a dulthood. Escaping mutant adults oftendisplay leg, antenna, and wing d eformities, presumably resulting from improper eversion of imaginal di scs. Sequence analysis indicates that 18w encodes a transmembrane prot ein with an extracellular moiety containing many leucine richrepeats a nd cysteine motifs, and an intracellular domain bearing homology to th e cytoplasmic portion of the interleukin-1-receptor. Expression of 18W protein in non-adhesive Schneider 2 cells promotes rapid and robust a ggregation of cells. Analysis of the expression of 18w in different mu tant backgrounds showsthat it is under control of segment polarity and homeotic genes. The data suggest that the 18W protein participates in the developmental program specified by segmentation and homeotic gene s as a cell ahesion or receptor molecule thatfacilitates cell movement s.