Fig. 3. Aberrant pathfinding in daw mutants. (A-C) Late stage 16/17 daw³ embryos labeled with (A) BP102, (B) 1D4 or (C) -Repo antibodies. Arrowheads mark rare CNS defects. (D,E) Schematic representation of motoneuron pathfinding in wild-type and daw^- embryos. Anterior is left, dorsal is up. Axon trajectories are depicted on the left and muscle targets are included on the right. (D) Five main nerve branches are shown that innervate correspondingly colored muscles. ISNb axons defasciculate to form three branches that innervate the muscle 6/7 cleft, muscle 13 and muscle 12. SNa forms a dorsal branch that innervates muscles 21-24 and a lateral branch that innervates muscles 5 and 8. For detailed description see Landgraf et al. (Landgraf et al., 1997). (E) In daw^- mutants the ISNb and SNa extend into their correct target fields, but terminate prematurely (black and white arrowheads, respectively). (F-I) Motoneuron projections in late stage 16/17 filleted embryos stained with 1D4. (F) Wild-type ISNb synapses on muscles 6/7, 13 and 12. (G) In daw³ embryos, ISNb stalls at muscle 13 (black and white arrowheads), or reaches muscle 12 but fails to form a synapse (arrow). (H) Wild-type SNa dorsal (d) and lateral (l) branches. (I) daw³ embryos displaying failure of SNa defasciculation and loss of the lateral branch (arrow). Arrowhead marks stalled axons. (J,K) Incidence of ISNb and SNa pathfinding defects in daw^- and Oregon R embryos. ISNb defects in J were scored as: stalling at muscles 6/7, muscle 13, or muscle 12 and failure to form a synapse. SNa defects in K were scored as: failure to reach target (short), or defasciculate at branchpoint (bifurcation). Hemisegments scored: daw¹ n=161/115, daw² n=300/233, daw³ n=222/221, daw⁴ n=238/200, daw maternal and zygotic nulls (MN) n=93/93, Oregon R n=155/178 for ISNb/SNa pathfinding.