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Fig. 7 Pk1 functions with Tri to mediate tangential neuronal migration. Dorsal views of hindbrains of embryos in which an isl1-GFP transgene labels cranial motor neurons (brown). Anterior to the left. Stage is indicated bottom left. (A,B) Expression of pk1 (blue) in relation to motor neurons (brown). The arrowheads indicate newly born (A) and migrating (B) facial motor neurons. pk1 is expressed at high levels anterior and posterior to the domain of facial motor neuron migration. In this domain, pk1 is expressed weakly in the vicinity of the migrating cells. (C-F) Wild-type embryo (C), embryo injected with 3 ng of pk1-Mo (D), tri heterozygous embryo (E) and tri heterozygous embryo injected with 1 ng of pk1-Mo (F). Migration of facial motor neurons (arrowheads) is disrupted in the embryo with severe abrogation of Pk1 function (D) and in the embryo with partial loss of Tri and Pk1 function (F). (G-J) Dorsal views of hindbrains of wild-type embryos (G,I) and of embryos injected with 3 ng of pk1-Mo (H,J). ot, otic vesicle; r3-5, rhombomeres 3-5.