Figure 2A NSC34cells were transiently transfected with expression vectors for V5-tagged wild-type and mutant PDIs. After 48 h, overexpressed PDI variants was assessed under reducing conditions in an 8% SDS-PAGE. An antibody detecting total PDIA1 (endogenous mousePDIA1 and exogenous humanV5-tagged PDIA1) (first panel). A second antibody detects only humanPDIA1, therefore only V5-tagged PDIA1 appears (second panel). A mouse and human specific antibody was used to detect total ERp57 (third panel). Anti-V5 was used to detect the exogenous PDI variants. Anti-β-actin was used as a loading control. B and C NSC34 cells were transiently transfected with the indicated PDIs constructs together with a GFP expression plasmid. Cell were then differentiated for 24 h in Neurobasal medium containing B27 supplement to induce cell differentiation. Increased neurite outgrowth is indicated with white arrow heads. B Quantification of the average primary neurite lengths was performed, all cells from three independent experiments were compiled. A minimum of 100 cells per experiment was analyzed. In addition, C the percentage of cells with neurites was quantified in the three independent experiments (right panel). B and C NSC34 cells were transiently transfected with the indicated PDIs constructs together with a GFP expression plasmid. Cell were then differentiated for 24 h in Neurobasal medium containing B27 supplement to induce cell differentiation. Increased neurite outgrowth is indicated with white arrow heads. B Quantification of the average primary neurite lengths was performed, all cells from three independent experiments were compiled. A minimum of 100 cells per experiment was analyzed. In addition, C the percentage of cells with neurites was quantified in the three independent experiments (right panel). D Primary rat ventral spinal cordneurons were prepared and after 4 daysin vitro (DIV) transfected with GFP alone or together with the indicated PDIs constructs. Cells were fixed at 10 DIV and SMI32 staining was performed to identify motoneurons. Images were taken and the total outgrowth of GFP and SMI32 positive cells was quantified. Results are compiled from 3 independent experiments. E Human motoneurons were differentiated from the human embryonic stem cell (ESC) HuESC 3 Hb9::GFP line. Differentiated neurons were transduced with lentivirus expressing GFP alone or together with PDIs-expressing plasmids. Transduced cells were cultured for another 10 days. To identify motoneurons after lentiviral transduction, immunocytochemistry analyses were performed. Quantification of neurite outgrowth in the different experimental conditions of GFP and HB9 positive neurons were obtained. Neurite number and assessment of the length of each neurite was performed in a similar manner as for primary rat motoneurons (see methods). Four independent experiments were performed. F NSC34 cell lines stably knocked down for PDIA1 or ERp57 were differentiated for 24 h in Neurobasal medium containing B27 supplement to induce cell differentiation. The percentage of cells with neurites was quantified in the three independent experiments. A minimum of 100 cells per experiment was analyzed.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.