Figure 5

Motor axon defects in triple mutants. Stage 16 or 17 embryos were stained with 1D4 and visualized using HRP immunohistochemistry. (a) In wild-type stage 16 embryos, ISN reaches its target and synapses with muscles 1 and 9 (asterisk) at a position distal to the tracheal dorsal trunk (shown in dotted lines). (b) In a Ptp4E Ptp10D; Ptp52F triple mutant embryo, ISN stalls at the second branch point (asterisk). (c) Wild-type SNa bifurcates (bifurcation point shown in arrowhead) and extends an anterior branch (left) and a posterior branch (right). (d-f) In Ptp4E Ptp10D; Ptp69D triple mutants, SNa shows various defects. Some branches are very thin (d, arrowhead) or almost undetectable (f, arrow). The branch on the right in (f, arrowhead) is normal. The left SNa in (e) has only stubs at the branchpoint (arrowhead). The SNa on the right abnormally projects beyond the muscle 22/23 bifurcation cleft and sends a thin projection toward an abnormal ISN side branch (e, asterisk). (g,h) The SNa in Ptp10D; Ptp69D embryos. Extra branch is shown on the anterior branch (g, asterisk), and a very short anterior branch is observed in (h, asterisk). (i) Wild type ISNb. At stage 17, synapses have begun to form at the muscle 12/13 cleft and at the bottom of muscle 13. (j) Ptp10D; Ptp69D stage 17 embryo shows ISNb branches with growth-cone-like morphologies that end at muscle 13. (k-m) ISNb defects in Ptp4E Ptp10D; Ptp69D triple mutants. (k) The ISNb on the right has an abnormal trajectory and stalls at muscle 13. (l,m) The same hemisegments, imaged in different focal planes. The characteristic clumped phenotype is seen in the left hemisegment (l, left arrow). The right hemisegment has a stall/bypass phenotype in which some ISNb axons grow out along the ISN, producing an ectopic branch onto muscle 12 (l, right arrow). In the middle hemisegment, thin branches also emerge from the clump and grow onto the surface of muscle 13 (m, arrowhead). Anterior is left and ventral is down in all panels. All scale bars are 10 microns.