Fig. 3. Semaphorin responses in different neuronal systems. (A) Bath application of embryonic chick dorsal root ganglion (DRG) neurons with Sema3A induces a rapid growth cone collapse response. Picture sequence shows images that were taken 2 minutes before and every 2 minutes after the application of Sema3A at 0 minutes (0'). Image courtesy of B.J.E. (B) Sema3F, expressed in Cos-cells, induces strong repulsion of axons extending from a rat hippocampal explant in a collagen gel assay. Image courtesy of A. Chedotal. (C) Mesodiencephalic dopaminergic (mdDA) neurons in the ventral tegmental area project their axons (green) in the medial forebrain bundle (MFB) rostroventrally through the developing diencephalon and telencephalon to innervate the prefrontal cortex (PFC). Innervation of the PFC is controlled by Class III semaphorins and their neuropilin receptors. Image courtesy of J. Pasterkamp. (D) Growth cones of the medial longitudinal fascicle (MLF) imaged in live transgenic zebrafish embryos. Axons extend normally in tightly bundled fascicles, whereas loss of either Sema3D or Tag1 disrupts fasciculation. Shown here is a morpholino knockdown of Tag1. Image courtesy of M. Halloran. (E) Side view of a neuropilin 1^-/- mouse embryo at E12.5 labeled with anti-neurofilament antibody. Loss of neuropilin 1 results in abnormal targetting of efferent projecting neurons. Image courtesy of H. Fujisawa.