Figure 5.
cAMP promotes regrowth of ventral synaptic branches in PLM. A, Regrowing axons in pde-4(lf) frequently extend ventrally directed branches (arrow) that reach the ventral cord; the depth-coded projection of confocal z-stack is shown. Surface focal planes are red, and deep planes are blue. The dotted line indicates the position of the section shown in F and F′. B, The total length of ventral branches is increased in pde-4 mutants; this effect is rescued by expression of PDE-4 under the control of the rab-3 or mec-4 promoters. C, Incubation in forskolin promotes PLM ventral branching in wild-type (muIs32) animals; both 100 and 500 μm forskolin promote ventral branching, although this is significant only for 500 μm (Kruskal–Wallis test). D, E, GFP::RAB-3 (jsIs821) is enriched at the tips of regrowing branches that reach the ventral cord (D, arrow) and not in branches that extend laterally (E, arrow); the pde-4(lf) background is shown. Autofluorescent scars from laser surgery are indicated. F, Electron micrograph of a regrown PLM branch (shaded yellow). F′, enlargement of the presynaptic area. White arrow, Electron dense zone; red arrow, ∼35-nm-diameter synaptic vesicle-like structure. Scale bars; A, D, E, 10 μm; F, F′, 100 nm. Statistics: t test; *p < 0.05; ***p < 0.001.