Figure 3(a-c). Drp1 is required for mitochondrial fission induced by PINK1. Drp1-null HeLa cells (Drp1KO) and their wildtype controls (Drp1WT) were co-transfected Δ110-PINK1-GFP-FKBP with FRB-MTS. Cells were induced with 250 nM rapalog for 2 hours to activate PINK1 kinase, followed by immunodetecting mitochondria (TOM20, red) and Δ110-PINK1-GFP-FKBP /FRB-MTS (Δ110-PINK1, green). Nuclei were labeled with DAPI (blue). Cells treated with solvent (DMSO) were used as a treatment control. Representative images were shown (a, upper panel, scale bar=25 μm). Higher magnification images are also included (a, lower panel, scale bar=10 μm). Mitochondrial morphology in different transfections was quantified. (b, c). Student's test. ***p<0.001, ns: no significance. Data was presented as mean ± SEM of three independent experiments. For each condition, >100 cells were analyzed. (d-f). Drp1S616 phosphorylation is required for mitochondrial fission induced by PINK1. Drp1KO HeLa cells were co-transfected Δ110-PINK1-GFP-FKBP /FRB-MTS with either a plasmid encoding Drp1WT or a Drp1 dephosphorylation mimic mutant Drp1S616A. Cells were treated with 250 nM rapalog for 2 hours to activate PINK1 kinase, followed by immunodetecting mitochondria (TOM20, blue), exogenous Drp1 (myc, red), Δ110-PINK1-GFP-FKBP /FRB-MTS (PINK1-FKBP, green). Cells treated with solvent (DMSO) were used as a treatment control. Representative images were shown, scale bar=25 μm (d). Higher magnification images are also included (d, Zoom, scale bar=5 μm). Mitochondrial morphology in different transfections was quantified (e, f). Student's test. **p<0.01, ***p<0.001, ns: no significance. Data was presented as mean ± SEM of three independent experiments. For each condition, >100 cells were analyzed. (g, h). Targeting PINK1 kinase domain to OMM increases mitochondrial localization of phosphorylated Drp1S616. HEK293 cells co-transfected FRB-MTS with Δ110-PINK1-GFP-FKBP were treated with 250 nM rapalog (Rapalog). After 2hours treatment, cytosol protion (cyto) and mitochondria (Mito) were fractionated and immunobloted with antibodies against either phospho (Ser616)-Drp1 (pS616), Drp1 (Drp1), or GFP (PINK1). Tom20 and β-actin were detected as mitochondrial loading control and cytosol loading control, respectively (g). Quantitation of pS616/Drp1 in various conditions was shown (h). Student's test. **p<0.01, ns: no significance. Data was presented as mean ± SEM of three independent experiments. (i, j). Targeting PINK1 kinase domain to the OMM increases mitochondrial localization of Drp1. HeLa cells co-transfected FRB-MTS with Δ110-PINK1-GFP-FKBP (FKBP-PINK1) were treated with 250 nM rapalog (Rapalog) for 2 hours to activate PINK1 kinase. Cells treated with solvent (DMSO) were included as a control. Cells were immunostained with antibodies against either Tom20, Drp1 and GFP (PINK1-FKBP). Representative images were shown, scale bar=2 μm (i). Higher magnification images from gated box are shown (bottom panels). Arrows indicate Drp1 puncta. Mitochondria-associated (yellow) and non-associated Drp1(Red) are shown, scale bar=1 μm. Mitochondria-associated Drp1 puncta were analyzed by using an ImageJ plugin-Coloc 2 and expressed as the Manders' Colocalization Coefficients (MCC) (j). Three different regions from each cell and >15 cells for each experimental group were analyzed. Student's test. **p<0.01. Data was presented as mean ± SEM of three independent experiments. (k, l). PINK1 regulates S616 and S637 phosphorylation of Drp1 via independent mechanisms. DRP1KO HEK293 cells co-transfected FRB-MTS/Δ110-PINK1-GFP-FKBP (PINK1WT) with either myc-Drp1WT or myc-Drp1S616A were treated with 250 nM rapalog (Rapalog) for 2 hours to activate PINK1 kinase. Cells treated with solvent (DMSO) were included as a control. Cell lysates were immunoblotting with antibodies against either phospho (Ser616)-Drp1 (pS616), phospho-(Ser637)-Drp1 (pS637), Drp1 and GFP (to detect PINK1-FKBP) (k). β-actin was detected as a loading control. Quantitation of pS637/Drp1 in various conditions was shown (l). One-way ANOVA followed with Tukey's test. ***p<0.001, ns: no significance. Data was presented as mean ± SEM of three independent experiments.