THE MAKING OF A FLY LEG - A MODEL FOR EPITHELIAL MORPHOGENESIS

Epithelial development dictates the shape of an organism. The metamorp hic development of a Drosophila leg precursor into an adult leg is a w ell-defined example of epithelial morphogenesis that can be analyzed f rom the perspectives of genetics and molecular and cell biology. The s teroid hormone 20-hydroxyecdysone induces and regulates the entire pro cess. Mutants affecting Drosophila leg morphogenesis characteristicall y have short thick legs (the malformed phenotype) resulting from a fai lure to execute normal cell shape changes at a specific stage of devel opment. Mutations that cause the malformed phenotype have already led to the identification and cloning of genes encoding transcription fact ors, a transmembrane serine protease presumably required for modificat ion of the apical extracellular matrix, and components of the contract ile cytoskeleton and adherens junctions. All of these products are req uired for the execution of normal changes in leg cell shape.