Fig. 3.

Schwann cell morphology during early regeneration is disrupted in lrp4 mutants. a Pre-transection 5 dpf, GFP-labeled sibling nerve stained with anti-Sox10 antibody labeling Schwann cell nuclei (magenta). Yellow arrowheads mark Schwann cell nuclei; scale bar 10 µm. b Sibling nerve 48 hpt labeled with GFP and stained with anti-Sox10 antibody. Yellow arrowheads mark Schwann cell nuclei. c Quantification of Schwann cell nuclei along individual nerves pre-transection and 48 hpt in siblings and lrp4 mutants. Pre-transection average Schwann cell number in siblings = 11.9 per nerve, n = 16 nerves; average Schwann cell number in lrp4 mutants = 10.78 per nerve, n = 36 nerves (two-tailed t-test p = 0.08, t = 1.743, df = 50; error bars denote mean and SD). Average Schwann cell number 48 hpt in siblings = 8.3 per nerve, n = 6 nerves; average Schwann cell number 48 hpt in lrp4 mutants = 9.3 per nerve, n = 6 nerves (two-tailed t-test p = 0.59, t = 0.5459, df = 10; error bars denote mean and SD). d–k Images from time lapse movies showing early regeneration dynamics in sibling (d–g) and lrp4 mutant (h–k) nerves. Motor axons express GFP, Schwann cells express mRFP (magenta). d Pre-transection sibling nerve, yellow box marks transection site. Schwann cell membranes (yellow arrowheads) are thin and closely associate with motor axons. White box indicates region magnified in (e–f). Scale bar 10 µm. e Magnified image showing granular Schwann cell morphology characteristic of a denervated Schwann cell (yellow arrowheads). f Schwann cell membranes revert to smooth pre-injury morphology (yellow arrowheads). Yellow box marks region magnified in (g). g Magnified image at same timepoint as (f), showing regenerating axons (green arrowheads) associating with flattened Schwann cell membranes (yellow arrowheads; n = 4/4 nerves). h Pre-transection lrp4 mutant nerve, yellow box marks transection site. Schwann cell membranes (yellow arrowheads) look wild type. White box indicates region magnified in (i–j). i Magnified image showing granular Schwann cell morphology (yellow arrowheads). j Lrp4 mutant Schwann cell membranes fail to revert to smooth pre-injury morphology (yellow arrowheads). Yellow box marks region magnified in (k). k Magnified image at same timepoint as j, showing a regenerating axon (green arrowhead) associating with granular Schwann cell membranes (yellow arrowheads; n = 7/8 nerves). l Pre-transection sibling nerve; yellow box marks transection site. m–o By 48 hpt, Schwann cell membranes form two thin, continuous tracks along which regenerating axons grow; white box indicates region magnified in n–o (filled yellow arrowheads mark Schwann cell membranes, green arrowheads mark regenerating axons; n = 23/24 nerves). p Pre-transection lrp4 mutant nerve; yellow box marks transection site. q–s By 48 hpt, Schwann cell membranes fail to form two thin, continuous tracks and remain granular; white box in (q) indicates the region magnified in r–s (filled yellow arrowheads mark continuous Schwann cell membrane track; open yellow arrowheads mark granular membranes; green arrowhead marks regenerating axon; n = 18/24 nerves)