Expression of ALS-linked variants of PDIA1 and ERp57 causes motoneuron dysfunction and impairs neurite outgrowth.Figure 1A Location of missense variants of PDIA1 and ERp57 identified in ALS cases. PDI primary structure: catalytic a and a' domains containing the active site motif CXXC sequence (dark purple and dark green), non-catalytic domains b and b' containing ligand binding sites (light purple and light green), and x-linker region (light gray). The constructs used in this study contained a V5-tag (orange) at the C-terminus that was inserted previous to the ER-retention signal (dark gray). B Expression of PDI variants in zebrafish. Zebrafish embryos at 1-2 cell stage were injected with sense mRNA coding for the indicated PDIs (PDIA1WT, PDIA1D292N and PDIA1R300H: 200 pg/embryo; ERp57WT, ERp57D217N and ERp57Q481K: 80 pg/embryo). Protein expression was confirmed by Western blot analysis using anti-V5 antibody in total embryo extracts at 24 h post-fertilization (hpf). Actin was used as a loading control. In the left panel 80 µg protein and in the right panel 120 µg protein extract were used. C and D, Motoneuron defects induced in zebrafish embryos after expression of the indicated ALS-linked PDI mutants and wild-type controls (PDIA1WT and PDIA1R300H: 80 pg mRNA/embryo; ERp57WT, ERp57D217N, ERp57D217N and ERp57Q481K: 30 pgtba mRNA/embryo). The most frequent global phenotypes induced by PDI injection are shown in lateral views of embryos at 24 hpf (left column). Black arrows indicate the presence of curly tail and/or shorter axis phenotypes (see details in Appendix Table S1). Axon motoneuron morphology was visualized using confocal microscopy in lateral views of the trunk region in transgenic Tg(Huc:Kaede) zebrafish at 36 hpf (middle and right columns). Images in the right column correspond to magnification views of the rectangular regions depicted in left and middle columns. Asterisks and arrows point to examples of increased axonal branching and reduced axonal length, respectively. C and D, Motoneuron defects induced in zebrafishembryos after expression of the indicated ALS-linked PDI mutants and wild-type controls (PDIA1WT and PDIA1R300H: 80 pg mRNA/embryo; ERp57WT, ERp57D217N, ERp57D217N and ERp57Q481K: 30 pgtba mRNA/embryo). The most frequent global phenotypes induced by PDI injection are shown in lateral views of embryos at 24 hpf (left column). Black arrows indicate the presence of curly tail and/or shorter axis phenotypes (see details in Appendix Table S1). Axonmotoneuronmorphology was visualized using confocalmicroscopy in lateral views of the trunk region in transgenic Tg(Huc:Kaede) zebrafish at 36 hpf (middle and right columns). Images in the right column correspond to magnification views of the rectangular regions depicted in left and middle columns. Asterisks and arrows point to examples of increased axonal branching and reduced axonal length, respectively. E and F Quantification of motoneuron axon length and axon branching in 36hpf Tg(Huc:Kaede) embryos injected with the indicated PDIA1 (D) and ERp57 (E) mutants. E and F Quantification of motoneuron axon length and axon branching in 36hpf Tg(Huc:Kaede) embryos injected with the indicated PDIA1 (D) and ERp57 (E) mutants. G Touch-evoked escape responses of 48 hpf zebrafish embryos injected with ALS-linked PDI mutants (Kabashi et al, 2011; Kabashi et al, 2009). The number of touches necessary to evoke an escape response (top) and speed (bottom, in mm/s) of the escape response was determined for each condition. The total number of analyzed embryos is indicated in parenthesis. Experiments of D-F were performed in selected animals sharing normal overall embryo morphology and viability, to avoid unspecific effects of axial shortening or curvature in motoneuron morphology and/or animal behavior. Statistical analyses were performed using one-way ANOVA and Bonferroni´s post hoc tests. Mean ± SEM with only statistically significant p values are shown: *, p ≤ 0.05; **, p ≤ 0.01; ***, p ≤ 0.001. Abbreviations: A (anterior), D (dorsal), P (posterior), V (ventral). Scale bars represent 500 m (C and D: a,d.g,j), 200 m (C and D: b,e,h,k), 100 m (C and D: c,f,i,l), and 25 µm (G-H).