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Fig. 4 The unipolar neurons express robo2 and make pathfinding errors in ast embryos. (A,B) Frontal views of the olfactory placode of 30-hpf omp:yfp/+ embryos. (A) Whole-mount in situ hybridization. Blue dots are signals for robo2 mRNA on the focal plane. Broad blue staining in the olfactory placode is derived from signals on cells that are out of the focal plane. (B) Double stainning for robo2 mRNA and YFP antigen. Early developing OSNs (arrows) and unipolar neurons (arrowheads) are stained in brown with anti-GFP antibody. Hybridization signals for robo2 mRNA (blue dots) are seen on the somata of both cell types. White dotted lines indicate the boundary between the olfactory placode and telencephalon. (C,D) Frontal views of the head of wild-type (C) and ast homozygous (D) embryos stained with zns-2 antibody at 36 hpf. The zns-2-positive axons misroute medially or ventromedially immediately after exiting the olfactory placode in ast embryos (arrows in D). Asterisks mark the position of the olfactory pit. d, dorsal; m, medial. Scale bar: 50 µm.