A CONSERVED SYSTEM FOR DORSAL-VENTRAL PATTERNING IN INSECTS AND VERTEBRATES INVOLVING SOG AND CHORDIN

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 cord(2), is function ally homologous to the chordin gene of Xenopus, which is expressed in the dorsal blastopore lip of the embryo and in dorsal mesoderm, in par ticular the notochord(3). We show by injections of messenger RNA that both sog and chordin can promote ventral development in Drosophila, an d that sog, like chordin(3), can promote dorsal development in Xenopus . In Drosophila, sog antagonizes the dorsalizing effects of decapentap legic (dpp)(1,2,4), member of the transforming growth factor-beta fami ly. One of the dpp homologues in vertebrates, bmp-4, is expressed vent rally in Xenopus(5) and promotes ventral development(6,7). We show tha t dpp can promote ventral fates in Xenopus, and that injection of sog mRNA counteracts the ventralizing effects of dpp. These results sugges t the molecular conservation of dorsoventral patterning mechanisms dur ing evolution.