Fig. 5. Loss of Gliolectin function delays pioneering of the longitudinal pathway. Pioneering of a longitudinal pathway is visualized with the mAb 1D4 (anti-Fasciclin II, nickel-enhanced) in wild-type (A-F), 
3013 homozygous (G-I) and glecm98/3013 (J-L) embryos at late stage 12 (A,D,G,J), early stage 13 (B,E,H,K) and late state 13 (C,F,I,L). In all panels, anterior is towards the left. The schematic diagrams across the top (A-C) depict the progressive completion of the pCC/MP1 pathway. At late stage 12, the pCC growth cone extends anteriorly towards the SP1 neuron (A, in all panels the arrow indicates site at which pCC meets the SP1 neuron). By early stage 13, the pCC growth cone has contacted the SP1 neuron (B, arrow) and continues to grow anteriorly to form a continuous longitudinal pathway by late stage 13 (C, arrow). The intensity of 1D4 staining increases from stage 12 through stage 13 in a pair of neurons at the midline (the dMP2/vMP2 pair, A-L, arrowhead), providing an independent assessment of nerve cord maturation. In the schematic diagram, the level of 1D4 staining is indicated by the shade of blue that colors the dMP2/vMP2 neuron cluster (A-C, arrowhead). In all other panels, the arrowhead indicates the position of the dMP2/vMP2 pair, although only one of each of these neurons is seen in the relevant focal plane. While dMP2/vMP2 staining is just barely detectable in stage 12 wild-type embryos (A,D, arrowheads), it progressively defines distinct neuronal boundaries by late 13 (C,F,I,L, arrowheads). In late stage 13 wild-type embryos, the pCC growth cone displays the streamlined morphology characteristic of a rapidly extending axonal process as it extends towards the point at which it will contact the SP1 neuron (D, arrow). In 3013 homozygotes at late stage 12, however, pCC axons do not extend as far as in wild type and frequently possess growth cones with spread morphology (G). By early stage 13, pCC frequently remains stalled within its segment of origin and continues to exhibit growth cone morphology more consistent with exploration than with fasciculation in 3013 homozygotes (H). In late stage 13 deletion homozygotes, pCC has extended into the next segment, although breaks in the pCC/MP1 pathway are frequently seen (I, arrow). In glecm98/3013 embryos, the absence of pCC extension is striking (J-L, arrow) even into late stage 13 (L, arrowhead indicates strong staining in vMP2/dMP2, a characteristic of the assigned stage). Scale bar: 5 µm in D-L.
