Fig. 6

Srrm4 knockdown rescues FBMN migration in rest mutants. (A) Model of Rest/Srrm4 regulation of FBMN maturation and the effect on FBMN migration. (B–E) Average projection dorsal views of 48 hpf FBMNs (green) in Tg(islet1:GFP) embryos immunolabeled with EphA4a to mark r5 (red). FBMN migration is unaffected in Srrm4 morphants (C) as compared to uninjected controls (B). MZrest^sbu29/sbu29 mutant FBMN migration (D) is partially rescued with knockdown of Srrm4 (E). (F) Quantitative counts of FBMN migration in r4 (black), r5 (checkered), and r6 (white) as % of all FBMNs. A significantly increased number of FBMNs migrate to r6 in MZrest^sbu29/sbu29 mutants injected with Srrm4 MO as compared to uninjected mutants. Mean±SEM; ^****P<0.0001. (G–J) Analysis of FBMNs at 22 and 30 hpf in Tg(zCREST1:membRFP);MZrest^sbu29/sbu29 embryos (G and H), and Tg(zCREST1:membRFP);MZrest^sbu29/sbu29 embryos injected with Srrm4 MO (I and J). Average morphological measurements from 5 embryos are shown at each stage (K–N). Mutants injected with Srrm4 MO have FBMNs that are more elongated than those injected with Control MO, and remain so at 30 hpf (K). They also send out fewer and shorter protrusions than MZrest^sbu29/sbu29 at both early and late stages (L–M). Mutants injected with Srrm4 MO have a smaller cytoplasmic volume compared to mutant controls at 22 hpf, which swells significantly at the later stage compared to the unchanged volume in MZrest^sbu29/sbu29 mutants (N).