Fig. 5. Lack of Fgf8 or Fgf3 results in aberrant axon trajectory and failure of commissure formation in the forebrain. (A-C) Diagrams depicting neuronal clusters (light brown) and axon tracts (dark brown) during zebrafish forebrain development [from information and diagrams in Wilson et al. and Ross et al. (Wilson et al., 1990; Ross et al., 1992)]. Lateral (D,G,J,M) or frontal (E,F,H,I,K,L,N,O) views focussed on the anterior and postoptic commissures following immunocytochemistry at 34 hpf with acetylated ß-tubulin antibodies. (D-F) Control embryos showing anterior and postoptic commissures. (G-I) Anterior commissure formation is defective in embryos injected with Fgf8mo. In some cases there is a complete failure of anterior commissure formation (H), and in other cases axons with abnormal trajectories (arrowhead) extend towards the midline (I). (J-L) Formation of both commissures is defective in embryos injected with Fgf3mo. In some cases, axons extend across the midline (arrowhead), partially forming commissures that are positioned abnormally close together (L). (M-O) There is a pronounced failure of commissure formation in the absence of both Fgf8 and Fgf3 (N). In severe cases, no axons enter the midline (O). ac, anterior commissure; drc, dorsorostral cluster; ep, epiphysis; npc, nuclei of the posterior commissure; poc, post-optic commissure; vcc, ventrocaudal cluster; vrc, ventrorostral cluster.