Fig. 2.

lrp4 is required non-cell-autonomously for axonal growth during regeneration. a Lateral view of a wild-type motor nerve labeled with GFP before laser transection at 5 dpf, with transection site marked by yellow box. Scale bar is 10 µm. b Six hours post transection (hpt), motor axons distal to the transection site have fully degenerated. c Forty-eight hours post transection, motor axons have regrown along their original path; green arrowheads indicate multiple regenerated fascicles; this representative nerve received a score of ‘best’ regeneration. d Lateral view of lrp4 mutant motor nerve labeled with GFP before laser transection at 5 dpf, with transection site marked by yellow box. e Six hours post transection, distal motor axons have fully degenerated. f Forty-eight hours post transection, motor axons have sprouted from the proximal stump but most fail to cross the injury site (open blue arrowheads); green arrowhead indicates stalled fascicle; this representative nerve received a score of ‘worst’ regeneration. g Quantification of nerve regeneration in wild type and lrp4 mutant larvae. In wild type, 85% of nerves regenerate “best” with two or more distinct fascicles (n = 26 nerves from 13 larvae). In lrp4 mutants, 70% of nerves regenerate zero or one fascicle (n = 28 nerves from 13 larvae) by 48 h post transection. Wild-type siblings regenerate significantly better than lrp4 mutants (χ²-test p < 0.0001, χ² = 18.48, df = 2). h Quantification of nerve regeneration in lrp4 mutant larvae and lrp4 mutant larvae expressing the motor neuron-specific mnx1:Lrp4-GFP transgene. At 48 hpt, lrp4 mutant larvae expressing Tg(mnx1:Lrp4-GFP) regenerate poorly (n = 15 nerves from 6 larvae), like lrp4 mutant larvae (n = 9 nerves from 4 larvae; χ²-test p = 0.9266, χ² = 0.1524, df = 2)