GOOSECOID EXPRESSION IN NEURECTODERM AND MESENDODERM IS DISRUPTED IN ZEBRAFISH CYCLOPS GASTRULAS

RNA from goosecoid, a homeobox-containing gene expressed during gastru lation in the anterior mesoderm of vertebrate embryos, can generate or ganizer activity when injected into ventral mesoderm, resulting in a s econdary body axis; it is not yet understood, however, how goosecoid p erforms its organizer function. We report here that in the zebrafish g astrula, a domain of goosecoid expression arises in presumptive anteri or neurectoderm which lies directly above goosecoid-expressing mesendo dermal cells. From this position, goosecoid expression then spreads gr adually across the ectodermal layer. In cyclops mutant embryos, which lack a ventral anterior brain, expression of goosecoid is abnormal in the mesendoderm and completely absent in the overlying neurectoderm. T hese results indicate that cyclops is required for correct specificati on of the mesendoderm and suggest that goosecoid expression in the ect oderm may result from vertical induction from the mesoderm. We propose that in the gastrula head, goosecoid may be important in organizing t he ventral neurectoderm. (C) 1994 Academic Press, Inc.