Forebrain mutants. A-X: Ventral views of zebrafish forebrains showing axons (αAT, green) and astroglial cells (αGfap, red). Anterior is up. A: WT forebrain commissures. Insets show POC (left) and the corresponding glial bridge (right) as single channels. Commissures and the optic chiasm all cross at the midline as cohesive bundles in direct association with glial bridges. B-X: Mutants with defects in forebrain astroglia and/or axonal anatomy. B: rrm2 mutants, known to have widespread necrosis, display severe astroglial reductions and dramatic optic nerve and commissural axon phenotypes including reductions and pathfinding errors. Mutants that had reduced or absent optic nerves include: (C) wnt5b, (D) gnl3, (E) bysl, (K) twistnb, (L,M) ppp1r12a, (N) utp11l, (O) mak16, (P) pou5f1,(Q) pes, (R) lamb1, (S) hnf1b, (T) abhd11, (U,V) esco2, and (W) kif11. Optic nerves were defasciculated in: (G) cdh2, (H) mpp5a, and (I) copa mutants. RGC axons made pathfinding errors in; (J) sfpq, (L) ppp1r12a, and (C) wnt5b mutants. Mutants having defasciculated commissures and/or axon pathfinding errors were; (C) wnt5b, (G) cdh2, (H) mpp5a, (L,M) ppp1r12a,(O) mak16, (P) pou5f1, (Q) pes, (R) lamb1, (S) hnf1b, (T) abhd11, (W) kif11, and (X) csnk1a1. The only mutants that did not exhibit astroglial patterning defects were (E) bysl, (G) cdh2, and (S) hnf1b. Insets show enlargements of boxed regions in the corresponding images. Arrows indicate mislocated axons phenotypes in the AC, POC (C,F,K-O), or optic nerves (S). Arrowheads highlight locations of specific axonal pathfinding errors (C,H-J,Q-T,W), astroglial defects (X), or the beginning of the optic nerves (F). White dots denote location of ectopic astoglial cell bodies at the forebrain ventricular zone (W, inset).