Fig. 5

shh overexpression does not induce branchiomotor neurons in dtr^te370a embryos. All panels show lateral views of the head, with rostral to the left and dorsal up, in embryos analyzed by islet1 (isl1; A-D) or netrin1a (net1a; E-H) in situ hybridization. Embryos at the 1- to 4-cell stage were injected with full-length lacZ (A,B,E,F) or shh (C,D,G,H) RNA, and fixed at 30 HPF. (A) In a lacZ-injected wildtype sibling, the clusters of nV, nVII and nX neurons (arrows) are evident. The asterisk denotes putative oculomotor (nIII) neurons in the midbrain. (B) In a lacZ-injected dtr^te370a homozygote, the branchiomotor, as well as the putative oculomotor, neurons are missing. (C) In a shh-injected wild-type sibling, a large number of ectopic isl1-expressing cells are induced throughout the hindbrain (arrows), which have been shown to be branchiomotor neurons (Chandrasekhar et al., 1998). (D) In a shh-injected dtrte370a homozygote, no isl1-expressing cells are induced in the hindbrain. (E) In a lacZ-injected wild-type sibling, net1a is expressed in the ventral half of the CNS throughout the embryo and in dorsoventral columns at rhombomere boundaries. (F) In a lacZ-injected dtr^te370a homozygote, net1a expression is normal. (G) In a shh-injected wildtype sibling, net1a expression in the CNS is expanded dorsally at all rostrocaudal levels. Supernumerary muscle pioneer cells expressing net1a are also evident in the somites, as described previously. (H) In a shh-injected dtr^te370a homozygote, net1a is ectopically expressed in the CNS and in the somites, in a similar fashion to injected wild-type embryos. Scale bar, 100 μm.