MUTATIONS IN THE SEGMENT POLARITY GENES WINGLESS AND PORCUPINE IMPAIRSECRETION OF THE WINGLESS PROTEIN

We have characterized the molecular nature of mutations in wingless (w g), a segment polarity gene acting during various stages of Drosophila development. Embryo-lethal alleles have undergone mutations in the pr otein-encoding domain of the gene, including deletions and point mutat ions of conserved residues. In a temperature sensitive mutation, a con served cysteine residue is replaced by a serine. In embryo-viable alle les, the wg transcriptional unit is not affected. Immunostaining of mu tant embryos shows that the embryo-lethal alleles produce either no wg antigen or a form of the protein that is retained within cells. Inter estingly, embryos mutant for the segment polarity gene porcupine show a similar retention of the wg antigen. We have also transfected wild t ype wg alleles into Drosophila tissue culture cells, which then displa y wg protein on the cell surface and in the extracellular matrix. In s imilar experiments with mutant alleles, the proteins are retained in i ntracellular compartments and appear not to be secreted. These data pr ovide further evidence that wg acts as a secreted factor and suggest t hat porcupine provides an accessory function for wg protein secretion or transport.