SECONDARY AXIS INDUCTION BY HETEROSPECIFIC ORGANIZERS IN ZEBRAFISH

To investigate the inductive activities of the vertebrate organizer, w e transplanted the chicken organizer (Hensen's node) into zebrafish ga strula and analyzed resulting secondary axes. Crafted Hensen's node di d not differentiate or participate in the secondary axis, It also did not induce a secondary notochord or expression of the genes normally e xpressed by the fish organizer including no tail, axial, goosecoid. Ne vertheless, it recruited fish cells to organize a variety of tissues: the dorsal portion of the central nervous system including Rohon-Beard sensory neurons, otic vesicles, dorsal pigment stripe, dorsal fin, so mites, heart, and pronephric ducts, Enlarged neural plate induced by t he organizer was shown by the expression pattern of dlx3 and msxB gene s, which demarcates the early presumptive neural tissue. In addition, Hensen's node of an earlier stage chicken embryo displayed differentia l movement in zebrafish from that of a later stage, This might reflect unknown differences in properties between the organizer at two differ ent developmental stages related to its normal organizer activity. To create a model system to study the molecular mechanisms of the organiz er, we next transplanted genetically modified mouse cells into zebrafi sh embryos. We found that Wnt3A-transfected NIH3T3 cells are much more potent in inducing a secondary axis than NIH3T3 cells alone, These re sults suggest that formation of a variety of tissues are controlled by signalling from the organizer itself with no requirement of participa tion of the organizer-derived tissues, Additionally, the activities of the organizer may involve a function of Wnt-family genes. (C) 1996 Wi ley-Liss, Inc.