The decapentaplegic [dpp] gene product, a TGF-p related ligand, acts as an extracellular moiphogen to establish at least two cellular response thresholds within the dorsal half of the Drosophila embryo. Null mutations in the screw {sew) gene are phenotypically similar to moderate dpp mutants and cause dorsal cells to adopt ventral fates. We show that sew encodes a novel TGF-p protein and is an integral part of the signal that specifies dorsal pattern. Although sew is expressed uniformly during

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... lastoderm stages, its effect on development appears graded and is restricted to the dorsal side of the embryo. Our results indicate that DPP activity alone is insufficient to specify different dorsal cell fates. We propose that SCW and DPP act together to establish distinct response boundaries within the dorsal half of the embryo, perhaps by forming heterodimers that have higher activity than homodimers of either molecule alone. The screw gene encodes a ubiquitously expressed member of the References http://genesdev.cshlp.org/content/8/21/2588.full.html#ref-list-1