Fig. 1. Brain phenotype of spg-embryos at pharyngula stages. (A,C,E,G,I) Wild-type and (B,D,F,H,J) homozygous spg mutant embryos. (A,B,E,F and small pictures in G,H) dorsal views; (C,D,G,H,I,J) lateral views. In the wild-type embryo (I), the MHB is marked by an arrow; The asterisk in B and the arrow in J indicate lack of the MHB in mutant embryos. (D,F) An arrowhead indicates a likely rudimentary tissue of the posterior cell row and the cerebellum after 28 hpf. (A,B) Phenotype of living embryos. (C-F) Optical sections of living embryos stained with fluorescent Bodipy-Ceramide. (G,H) Fluorescent staining with Acridine Orange indicates cell death at the prospective MHB and the optic stalk in spg embryos (H) at the 17-somite stage, indicated by arrows. Cell death is also detected in two transverse bands within the rhombencephalon at the 22-somite stage (arrowheads, insert in H; the arrow points to the MHB). (I,J) Sagittal histological sections.