Originally published as Genetics Published Articles Ahead of Print on December 1, 2005.

Genetics, Vol. 172, 1577-1593, March 2006, Copyright © 2006
doi:10.1534/genetics.105.047100

Mutational Analysis of Stubble-stubbloid Gene Structure and Function in Drosophila Leg and Bristle Morphogenesis

Ann S. Hammonds and James W. Fristrom1

Department of Molecular and Cell Biology, University of California, Berkeley, California 94720

1 Corresponding author: Department of Molecular and Cell Biology, 569 Life Science Addition, University of California, Berkeley, CA 94720-3200.
E-mail: jfristro{at}calmail.berkeley.edu

The Stubble-stubbloid (Sb-sbd) gene is required for ecdysone-regulated epithelial morphogenesis of imaginal tissues during Drosophila metamorphosis. Mutations in Sb-sbd are associated with defects in apical cell shape changes critical for the evagination of the leg imaginal disc and with defects in assembly and extension of parallel actin bundles in growing mechanosensory bristles. The Sb-sbd gene encodes a type II transmembrane serine protease (TTSP). Here we use a Sb-sbd transgenic construct to rescue both bristle and leg morphogenesis defects in Sb-sbd mutations. Molecular characterization of Sb-sbd mutations and rescue experiments with wild-type and modified Sb-sbd transgenic constructs show that the protease domain is required for both leg and bristle functions. Truncated proteins that express the noncatalytic domains without the protease have dominant effects in bristles but not in legs. Leg morphogenesis, but not bristle growth, is sensitive to Sb-sbd overexpression. Antibody localization of the Sb-sbd protein shows apical expression in elongating legs. Sb-sbd protein is found in the base and shaft in budding bristles and then concentrates at the growing tip when bristles are elongating rapidly. We propose a model whereby Sb-sbd helps coordinate proteolytic modification of extracellular matrix attachments with cytoskeletal changes in both legs and bristles.