Fig. 6

(A-D) Effects on primary neurogenesis following injection of X-Delta1 or X-Delta1^dn RNA, together with lacZ RNA as a marker, into one blastomere. Flat-mounted embryos at 5- to 6-somite stage, with islet1 expression in purple-blue, lacZ marker in sky-blue; lowmagnification views on the left, details on the right; note that the Xgal treatment of the embryos for detection of lacZ product results in fainter in situ hybridisation stainings than in Figs 2-5. X-Delta1 inhibits production of all classes of islet1-positive primary neurons in the injected (sky-blue) region; X-Delta1^dn does the opposite. Arrowheads in B indicate a few Rohon-Beard cells that have been formed despite the injected X-Delta1. Note that convergence movements and folding of the neural plate lead to cell mixing in the midline, so that motor neuron production appears affected uniformly on both sides of the midline. tg, trigeminal ganglion; mn, motor neurons; RB, Rohon-Beard neurons. (E,F) Effects on primary neurogenesis following injection of deltaB RNA, together with lacZ RNA as a marker, into one blastomere. Flat-mounted embryos at 5- to 6-somite stage, with islet1 expression in purple-blue, lacZ marker in sky-blue; low magnification views on the left, details on the right. Where deltaB RNA is present, production of islet1-positive primary neurons is inhibited. Scale bars: 200 μm (A,C,E), 100 μm (B,D,F).