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doi: 10.1242/10.1242/dev.00161

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Regulation of Easter activity is required for shaping the Dorsal gradient in the Drosophila embryo

Andy J. Chang^* and Donald Morisato^,

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
^* Present address: Department of Anatomy, University of California, San Francisco, CA 94143, USA
Present address: The Evergreen State College, Lab I Room 3009, Olympia, WA 98505, USA

Author for correspondence (e-mail: donaldm{at}evergreen.edu)

Accepted 21 August 2002

Dorsoventral polarity of the Drosophila embryo requires maternal spätzle-Toll signaling to establish a nuclear gradient of Dorsal protein. The shape of this gradient is altered in embryos produced by females carrying dominant alleles of easter (ea^D). The easter gene encodes a serine protease that generates processed Spätzle, which is proposed to act as the Toll ligand. By examining the expression domains of the zygotic genes zen, sog, rho and twist, which are targets of nuclear Dorsal, we show that the slope of the Dorsal gradient is progressively flattened in stronger ea^D alleles. In the wild-type embryo, activated Easter is found in a high M_r complex called Ea-X, which is hypothesized to contain a protease inhibitor. In ea^D embryo extracts, we detect an Easter form corresponding to the free catalytic domain, which is never observed in wild type. These mutant ea^D proteins retain protease activity, as determined by the production of processed Spätzle both in the embryo and in cultured Drosophila cells. These experiments suggest that the ea^D mutations interfere with inactivation of catalytic Easter, and imply that this negative regulation is essential for generating the wild-type shape of the Dorsal gradient.

Key words: Dorsoventral polarity, easter, spätzle, dorsal, Serine protease, Drosophila