Antimorphic goosecoids.

goosecoid (gsc) is a homeobox gene expressed in the Spemann organizer that has been implicated in vertebrate axis formation. Here antimorphic gscs are described. One antimorphic gsc (MTgsc) was fortuitously created by adding 5 myc epitopes to the N terminus of gsc. The other antimorph (VP16gsc) contains the transcriptional activation domain of VP16. mRNA injection of either antimorph inhibits dorsal gastrulation movements and leads to embryos with severe axial defects. They upregulate ventral gene expression in the dorsal marginal zone and inhibit dorsal mesoderm differentiation. Like the VP16 domain, the N-terminal myc tags act by converting wild-type gsc from a transcriptional repressor into an activator. However, unlike MTgsc, VP16gsc is able at low dose to uncouple head from trunk formation, indicating that different antimorphs may elicit distinct phenotypes. The experiments reveal that gsc and/or gsc-related genes function in axis formation and gastrulation. Moreover, this work warns against using myc tags indiscriminately for labeling DNA-binding proteins.