1. ^*Department of Molecular Genetics and Cell Biology, University of Chicago, 920 East 58th Street, Chicago, Illinois 60637, USA
2. ^ᤠMcArdle Laboratory for Cancer Research and Laboratory of Genetics, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA
3. ^á¤Department of Biological Chemistry and Howard Hughes Medical Institute, University of California, Los Angeles, California 90024, USA

Abstract

DORSAL-VENTRAL patterning within the ectoderm of the Drosophila embryo requires seven zygotic genes, including short gastrulation (sog)¹. Here we demonstrate that sog, which is expressed in the ventrolateral region of the embryo that gives rise to the nerve cord², is functionally homologous to the chordin gene of Xenopus, which is expressed in the dorsal blastopore lip of the embryo and in dorsal mesoderm, in particular the notochord³. We show by injections of messenger RNA that both sog and chordin can promote ventral development in Drosophila, and that sog, like chordin³, can promote dorsal development in Xenopus. In Drosophila, sog antagonizes the dorsalizing effects of decapentaplegic (dpp)^1,2,4, a member of the transforming growth factor- family. One of the dpp homologues in vertebrates, bmp-4, is expressed ventrally in Xenopus⁵ and promotes ventral development^6,7. We show that dpp can promote ventral fates in Xenopus, and that injection of sog mRNA counteracts the ventralizing effects of dpp. These results suggest the molecular conservation of dorsoventral patterning mechanisms during evolution.