THE FRIZZLED GENE OF DROSOPHILA ENCODES A MEMBRANE-PROTEIN WITH AN ODD NUMBER OF TRANSMEMBRANE DOMAINS

The protein encoded by the Drosophila tissue polarity gene, frizzled (fz), is required for both the intercellular transmission and the intracellular transduction of a tissue polarity signal. In order to study the biochemical characteristics of this rare protein, we constructed a hs-fz fusion gene and transferred this to Drosophila tissue culture cells and embryos. Cell fractionation experiments and immunostaining experiments showed that the Fz protein is an integral membrane protein containing an odd number of transmembrane domains, consistent with previous suggestions that it contains seven transmembrane domains. Immunostaining of pupal wings showed that the Fz protein is evenly distributed throughout the wing arguing that the Fz protein does not act as a graded morphogen.