EMBO/SourceData huggingface dataset:
Figure 3A,B, No difference in voltage dependent Ca2+-currents (A) and fractional activation of ICa-channels (B) between OtofI515T/I515T IHCs (n=16) and IHCs of Otof+/+ littermates (n=13).C, Exocytosis was recorded by measures of changes in membrane capacitance (ΔCm, lower panel) in response to depolarization (left, 20ms; right, 100ms) to the voltage where maximum Ca2+-currents were elicited (upper panel), typically -14mV.D, Upper panel, while for stimuli up to 20ms exocytosis from OtofI515T/I515T (n=13) and Otof+/+ (n=11) IHCs was similar, sustained exocytosis, representing most likely the release of replenished vesicles, was significantly reduced in OtofI515T/I515T IHCs (t-test). Lower panel, Ca2+-current integrals were of similar size.E, Flash photolysis of caged Ca2+ elicited a smaller exocytic response in OtofI515T/I515T IHCs.F, The kinetics of the fast component from E was comparable between OtofI515T/I515T IHCs and Otof+/+ littermates (b). Open circles represent previously published data on IHCs of hearing wild-type mice (a; Beutner et al, 2001; Pangrsic et al, 2010).
Figure 4A, Spontaneous rates of SGNs from OtofI515T/I515T (red, n=35) and Otof+/+ littermates (black, n=39) were not significantly different (p=0.83, Kolmogorov-Smirnov test).B-D, Averaged poststimulus time histograms ±SEM from OtofI515T/I515T mice (n=25-32) and Otof+/+ littermate SGNs (n=13-27) to stimulation with 50ms tone bursts at the characteristic frequency (CF) of each fiber, 30dB above threshold at indicated stimulus rates.E, Quantification of onset (largest 0.5ms bin, Mann-Whitney U test) and adapted responses (averaged 35-45ms from response onset, t-test) from data in B-D.F, The jitter of the first sound-evoked spike was significantly increased (p<0.001, Mann-Whitney U test) but retained its inverse correlation with spike rates.G, Spike rate increases with rising stimulus intensity were significantly shallower in OtofI515T/I515T SGNs, both for repetitive stimulation with 50ms tone bursts (left, p=0.014, t-test) and for continuous stimulation with amplitude modulated tones (right, p<0.001, Mann-Whitney U test).H, Phase locking to amplitude modulated tones (assessed as the maximal synchronization index) was typically less precise in OtofI515T/I515T SGNs than in Otof+/+SGNs (p=0.09, Mann-Whitney U test).I, 100ms masker tone and 15ms probe tones (both at CF, 30dB above threshold) were separated by silent intervals of variable duration. Inter-masker intervals were 500ms for Otof+/+, and 1000ms for OtofI515T/I515T. The ratio of probe and masker onset responses revealed enhanced RRP depletion after stimulation in OtofI515T/I515T (pink; mean ±SEM red) compared to Otof+/+ (grey; mean ±SEM black; for 4ms interval: p=0.001, t-test) and a slowed time course of recovery (x: half time of recovery, taken from normalized recovery functions; p<0.001, Mann-Whitney U test).K, Mice learned to drink water when continuous noise was present but avoided drinking when the noise was interrupted by silent gaps. 5 OtofI515T/I515T mice (pink, mean ±SEM red) avoided drinking less efficiently than 2 Otof+/+ mice (grey, mean ±SEM black) for shorter gap durations. See also Figs S2/S3.
Figure 5A, Exemplary ABR traces (Click 100dB) from one OtofI515T/I515T mouse recorded at indicated bullatemperatures during local heating. Note that ABRs never disappeared completely, but wave I amplitude changed reversibly with temperature.B,C, ABR wave I amplitudes in OtofI515T/I515T (A, Click 100dB) and Otof+/+ mice (B, Click 80dB) decreased with increasing temperature in the bulla. Each color represents a different experiment, dashed lines are line fits. Open symbols indicate the beginning of the experiments; subsequent recordings are connected by lines. The four indicated data points in B correspond to ABRs in A.D, Explanted organ of Corti from an Otof+/+ mouse at P4 after two days in vitro (DIV2) at 37°C immunostained against otoferlin (magenta) and Vglut3 (green). Note the intense immunostaining of otoferlin at the plasma membrane. Scale bar 10 µm.E-J, Explanted organs of Corti from Otof-/- mice at P4 were transfected by GeneGun with otoferlin cDNA and eGFP and immunostained at DIV2.E, Example cell transfected with wild-type mouseotoferlin cDNA.F,G, Representative cells transfected with mouseotoferlin including the 20 amino acids of the RXR motif (see Fig EV4). Cells in G were incubated at 38.5°C for 30 min prior to fixation. The RXR-otoferlin transfected cells show a membrane localization of otoferlin surrounding the Vglut3 immunofluorescence/eGFP fluorescence at the basal pole of the cells (arrows), similar as in controls (A,B).H,J, Both the human RXR motif and the Ile515Thr mutation were introduced in mouse cDNA, and cells were incubated at 37°C (H) or for 30min at 38.5°C (J) before fixation. Here, green fluorescence surrounds the otoferlin immunofluorescence (arrows), suggesting loss of otoferlin from the plasma membrane.K, Quantification of the relative plasma membrane levels of otoferlin (as in Fig 1) revealed normal plasma membrane abundance when the human RXR motif was present, but a strong reduction for otoferlin with RXR and Ile515Thr (individual cells; mean ±SEM; t-test).
Figure 6A-E, Capacitance increments recorded from Otof+/+ (black) and OtofI515T/I515T (red) IHCs. Individual cells recorded at indicated temperatures (light circles), mean ±SEM for perforated patch clamp experiments (t-test).F,G, Summary of the capacitance changes and Ca2+-current integrals for Otof+/+ (F) and OtofI515T/I515T IHCs (G) at the different temperatures illustrates the drastic increase in exocytosis for physiological temperature. *Significant differences compared to RT measurements are indicated with colors of the respective temperature, and between PT and high temperature in violet (t-test).H-J, Otoferlin immunofluorescence in Otof+/+ IHCs (upper panel) and OtofI515T/I515T IHCs (middle and lower panels) of explanted organs of Corti at P7-P8 after incubation at indicated temperatures for 24h; maximum projections of z-stacks, inverted images, scale bar 10µm. The same imaging settings have been applied in all experiments, and the same lookup table was applied for the upper and middle panels. Images of lower panels are enhanced compared to middle panels (lookup table covering full data range of only this genotype) to visualize otoferlin distribution.H-J, Otoferlin immunofluorescence in Otof+/+ IHCs (upper panel) and OtofI515T/I515T IHCs (middle and lower panels) of explanted organs of Corti at P7-P8 after incubation at indicated temperatures for 24h; maximum projections of z-stacks, inverted images, scale bar 10µm. The same imaging settings have been applied in all experiments, and the same lookup table was applied for the upper and middle panels. Images of lower panels are enhanced compared to middle panels (lookup table covering full data range of only this genotype) to visualize otoferlin distribution.K, Quantification of otoferlin immunofluorescence in Otof+/+ IHCs (black bars, n=98-137 cells, 4-5 experiments) and OtofI515T/I515T IHCs (red bars, n=90-97 cells; Kruskal-Wallis test as in L-N), indicate reduced protein levels with increasing temperature.L, Apical/basal otoferlin protein distribution, revealing a significant apical shift of otoferlin and Vglut3 for OtofI515T/I515T IHCs (red symbols) at 38.5°C compared to Otof+/+ (grey/black symbols).M, Relative levels of membrane bound otoferlin were lowered with increasing temperature.N, Absolute otoferlin membrane immunostaining strongly decreased with temperature.
Figure 7A-C, Pre-embedding immunogold labelling for EM visualizes otoferlin localization in random ultrathin sections through the basal part of IHCs in Otof+/+ (A) and OtofI515T/I515T (B) but not in Otof-/- (C) mice. IHCs are highlighted in beige. Scale bar 100nm.D-G, Magnified synaptic ribbons (R) and postsynaptic afferent boutons of SGNs (Aff), displaying otoferlin immunogold labelling at active zone membranes (pink arrowheads) but not around the synaptic ribbon, using saponin permeabilization (D-F), or Triton-X-100 treatment (G).H, Vglut3 immunogold labelling adjacent to the ribbon as expected for synaptic vesicle. Scale bar 200nm.I,J, Some otoferlin labelled structures bear clathrin coats (red arrowheads), suggesting that they originate from bulk endocytosis. Scale bar 100nm.K, Otoferlin labelled vesicles were on average larger in OtofI515T/I515T IHCs (OtofI515T/I515T, n=86 vesicles, 18 images; Otof+/I+, n=82 vesicles, 6 images; Wilcoxon-rank-sum-test, as in L-M).L, Quantification of immunogold clusters at the plasma membrane revealed a strong trend towards reduced levels of otoferlin in OtofI515T/I515T (6 images each).M, Distal from the plasma membrane, immunogold labels were reduced in OtofI515T/I515T IHCs.N, Representative electron micrographs of IHCribbon synapses in OtofI515T/I515Tand Otof+/ (conventional embedding without immunogold) after pre-incubation for 10min at the indicated temperature followed by high K+ stimulation or 0 Ca2+ inhibition for 1min 45sec. Scale bars 100nm.P-Q, Synaptic vesicles with >45 nm diameter appeared at 39°C in random sections; fraction of large membrane-proximal (P; Kruskal-Wallis test) and ribbon-associated (Q; one way ANOVA followed by Tukey's test) synaptic vesicles (see also Appendix Table S1).
Figure 8A-D, Exemplary virtual sections through EM tomograms for stimulatory condition at 36°C and 39oC. Scale bar 100nm.F-I, 3D reconstruction of the ribbon-associated pool of vesicles (front view). Active zone membrane is depicted in blue, presynaptic density in pink, and ribbons in red, scale bars 100nm.F-I, 3D reconstruction of the membrane-proximal pool (top view) and J-M, the ribbon-associated pool of vesicles (front view). Active zone membrane is depicted in blue, presynaptic density in pink, and ribbons in red, scale bars 100nm.N-Q, Cumulative probability distribution of the diameter of round vesicles as well as the longest axis of flattened vesicles in the membrane-proximal pool (N-O) and ribbon-associated pool (P-Q). N-P, one way ANOVA followed by Tukey's test; Q, Kruskal-Wallis test. Round vesicles tested in both the pools appeared larger in OtofI515T/I515T IHC synapses but the long axis of flattened vesicles were comparable for both the genotypes (see also Table EV1).
Figure 1(A) Rescue of growth phenotype. Wild-type (WT) or mdm10Δ cells were transformed with the empty plasmid pYX142 (). In addition, mdm10Δ cells were transformed with pYX142 encoding MDM10 or MCP3. Cells were grown to an OD600 of 1.0 and spotted on YPD or YPG plates in a 1:5 dilution series. Plates were incubated for growth at the indicated temperatures.(B) Over-expression of Mcp3 partially rescues the mitochondrial morphology defect in mdm10Δ cells. Cells described in (A) expressing mitochondrially targeted GFP (mtGFP) were analysed by fluorescence microscopy. Typical images (fluorescence and brightfield, BF) of the four different strains are shown (scale bar = 5 µm). The quantification shows the average percentage with standard deviation bars of three independent experiments (n=3; SD; *, p < 0.05 and as indicated) with at least 100 cells per experiment.
Figure 2(A) Respiratory chain super-complex levels are slightly restored by over-expression of Mcp3. Mitochondria isolated from the indicated strains were lysed in 1% digitonin and subjected to a 4-8% BN-PAGE. Proteins were analysed by immunodecoration with antibodies against either Cor1 of complex III or Cox2 of complex IV.(B) Assembly defects in TOM and TOB complexes in mdm10 cells are partially restored by Mcp3 over-expression. Mitochondria of the indicated cells were lysed in 1% digitonin and subjected to a 6-13% BN-PAGE and immunoblotting with antibodies against Tom40 (left) or Tob55 (right). The assembled TOM complex and an unassembled Tom40 species at ca. 100 kDa (arrowhead) are indicated as well as the TOB complex and an additional higher molecular weight species of the TOB complex (asterisk).(C) Over-expression of Mcp3 partially rescues the alterations in lipid composition of cells lacking Mdm10. Lipids were extracted from highly pure mitochondria isolated from the indicated cells and then analysed by mass spectrometry analysis. The level of each phospholipid species in wild-type mitochondria was set to 100% and the ERG/PL ratio to 1. Relative changes in mitochondria from other cells are presented. The mean with standard deviations of three biological repeats with two technical repeats for each (n=6; SD; *, p < 0.05) is given.(D) Mcp3 rescues loss of Mdm12. Wild-type (WT) or mdm12Δ cells transformed with the empty plasmid pYX142 () or mdm12Δ cells over-expressing either Mcp3 or Mdm12 (as a control) were analysed at 30°C or 37°C by drop dilution assay on rich medium containing glycerol (YPG).(E) Mcp3 rescues loss of Mmm1. WT and mmm1Δ cells were transformed and analysed as described in (D).(F) Mcp3 rescues loss of Mdm34. WT and mdm34Δ cells were transformed and analysed as described in (D).
Figure 3(A) Growth phenotype of mcp3 cells. WT or mcp3∆ cells were grown to an OD600 of 1.0 in YPD medium and spotted on YPD or YPG plates in a 1:5 dilution series. Plates were incubated for growth at the indicated temperatures.(B) mcp3 cells have normal mitochondrial morphology. WT and mcp3∆ cells expressing mitochondrially targeted GFP (mtGFP) were grown to mid-logarithmic phase then analysed by fluorescence microscopy. Typical images of the two different strains are shown (scale bar = 5 µm). The quantification of the depicted strains shows the average percentage with standard deviation bars of three independent experiments with at least 100 cells per experiment (n=3; SD; p as indicated).(C, D) Loss of Mcp3 has no effect on the phospholipid composition of mitochondria. Highly-pure mitochondria were isolated from the indicated yeast cells. Lipids were extracted and then analysed by mass spectrometry analysis. The level of each phospholipid species in wild-type mitochondria was set to 100% and the ERG/PL ratio to 1. Relative changes in mitochondria from mcp3 cells are presented. The mean with standard deviations of three biological repeats with two technical repeats for each (n=6; SD) is given.(E) Over-expression of Mcp3 leads to alterations of the tubular mitochondrial network. Wild-type cells expressing mitochondrially targeted GFP (mtGFP) were transformed with a plasmid over-expressing Mcp3 (MCP3) or an empty plasmid as control (). Cells were grown to mid-logarithmic phase and then analysed by fluorescence microscopy. Typical images of the two different strains are shown (scale bar = 5 µm).
Figure 5(A) Isolated mitochondria were incubated with radiolabelled Mcp3 precursor protein for the indicated time periods. After import mitochondria were reisolated and analysed by SDS-PAGE and autoradiography. The arrowhead marks an additional band of the size of the cleaved N-terminus of Mcp3. p and m, precursor and mature forms, respectively.(B) Import of Mcp3 is dependent on the receptor Tom70. Mitochondria isolated from wild-type or tom70/71Δ cells were incubated with radiolabelled Mcp3 or pSu9-DHFR (as control) for the indicated time periods. After import mitochondria were reisolated and analysed by SDS-PAGE and autoradiography. p and m, precursor and mature forms, respectively. I, 20% of radiolabelled precursor protein used in each import reaction. Bands corresponding to the mature (m) form were quantified. Import into wild-type mitochondria after 15 min was set to 100%. The mean with standard deviations is depicted (n=3; SD).(C) Reduced steady state levels of HA-Mcp3 in cells lacking Tom70. Crude mitochondria isolated from the indicated cells were analysed by SDS-PAGE and immunodecoration with antibodies against the HA-tag, AAC as control substrate of Tom70, and Fis1 as a loading control. HA-Mcp3 levels were quantified in relation to Fis1 levels and the levels in WT cells were set to 100%. The bar diagram shows the mean with standard deviation (n=3; SD; *, p < 0.05).(D) Import of Mcp3 is dependent on Tom40. Mitochondria isolated from wild-type and tom4025 cells were incubated with radiolabelled Mcp3 for the indicated time periods. Next, mitochondria were reisolated and analysed by SDS-PAGE and autoradiography as described in (B). As a control Ugo1 was imported into the same mitochondria. Organelles were reisolated and analysed by BN-PAGE and autoradiography. The band corresponding to the Ugo1 dimer at around 150 kDa was quantified. The mean with standard deviation is shown (n=3; SD).(E) Steady state levels of HA-Mcp3 are lower in cells harbouring a mutant TOM40 allele. Crude mitochondria from wild-type and tom40-25 cells were obtained and analysed as described in (C). Immunodecoration was performed with antibodies against the HA-tag, Tom40, and Fis1 as loading control.
Figure 6(A) Mcp3 precursor binds in vitro to cytosolic domains of TOM receptors. Radiolabelled Mcp3 was incubated with recombinant GST alone or GST fused to the cytosolic domains of Tom70, Tom20 or Tom22 prebound to glutathione beads or with unloaded beads. After washing bound material was eluted with sample buffer. Proteins were analysed by SDS-PAGE, blotting onto a membrane and autoradiography. To demonstrate equal amounts of GST fusion proteins the membrane was stained with Ponceau S. I, input 5% of precursor used.(B) Mcp3 precursor binds to Tom22 in organello. Radiolabelled Mcp3 was incubated with mitochondria isolated from WT His-Tom22 containing cells. Mitochondria were pre-incubated with CCCP (40 µM) to halt import. After lysis with β-dodecyl maltoside samples were incubated with Ni-NTA beads. After washing bound proteins were eluted with sample buffer and analysed by SDS-PAGE and autoradiography. I, 5% of 35S-Mcp3 used; pel., 2% insoluble material after clarifying spin; sup., 2% of material incubated with Ni-NTA; n.b. 2% of non-bound material after binding to Ni-NTA; eluate, 100% of bound material.(C) Radiolabelled Mcp3 was incubated with organelles described in (B). After import mitochondria were solubilized in digitonin, the lysate was cleared by centrifugation and incubated with or without an antibody against the His-tag (α-His). Samples were analysed by BN-PAGE, autoradiography and afterwards immunodecoration with an antibody against Tom40. Bands shifted by the anti-His antibody are indicated by arrowhead.
Figure 7(A) Import of Mcp3 is dependent on the TIM23 complex. Mitochondria isolated from wild-type and tim23ts cells were incubated with radiolabelled Mcp3 for the indicated time periods. Further treatment and analysis (n=3; SD) was as described for Fig. 5D.(B) Steady state levels of HA-Mcp3 are lower in cells harbouring a temperature sensitive TIM23 allele. Crude mitochondria were obtained at the non-permissive temperature from WT or tim23ts cells containing a plasmid expressing HA-Mcp3. Samples were analysed by SDS-PAGE and immunodecoration with antibodies against the HA-tag, the matrix proteins Mge1 and Yah1 as typical TIM23 substrates, Ugo1 and Fis1 as TIM23-independent substrates. HA-Mcp3 levels were quantified in relation to Fis1 levels. Levels in WT cells were set to 100%. The bar diagram shows the mean with standard deviation of six independent experiments (n=6; SD; **, p < 0.01).(C) Import and processing of Mcp3 is dependent on the mitochondrialmembrane potential. Isolated mitochondria were incubated with radiolabelled Mcp3 or pSu9-DHFR as control for the indicated time periods or for 15 minutes in the presence of either CCCP or o-phenantroline and EDTA (o-Phen./EDTA). After import mitochondria were reisolated and analysed by SDS-PAGE and autoradiography. L+MPP: radiolabelled proteins were incubated with recombinant MPP.(D) Mcp3 is processed by Imp1/2. Single deletion strains of known mitochondrial proteases and peptidases were transformed with a plasmid expressing HA-Mcp3. Crude mitochondria were isolated and analysed by SDS-PAGE and immunodecoration with antibodies against the indicated proteins and the HA-epitope. Cox2, a known substrate of IMP; Tom70, a mitochondrial outer membrane protein.(E) C-terminally tagged Mcp3-HA is processed by Imp1. WT and imp1Δ cells were transformed with a plasmid expressing Mcp3-HA and further analysis was performed as described in (D).(F) Mcp3 is processed by Imp1/2 after in vitro import into mitochondria. Mitochondria isolated from WT, imp1Δ or imp2Δ strains were incubated with radiolabelled precursor of Mcp3 or pSu9-DHFR as control. Further treatment and analysis was as described in Fig. 5A.(G) Full-length Mcp3 precursor accumulates during import if IMP processing is abolished. Radiolabelled internally HA-tagged Mcp3 without (HA-Mcp3) or with mutation in the Imp1 cleavage site (D70G+HA) were incubated with mitochondria as in (F). After import samples were incubated with or without PK (20 µg/ml). Samples were analysed by SDS-PAGE and autoradiography.(H) Mitochondrial membrane potential is required for efficient import of Mcp3 precursor into mitochondria. Isolated mitochondria were incubated with radiolabelled Mcp3 in the presence or absence of CCCP. After import mitochondria were incubated with PK as in (G) and analysed by SDS-PAGE and autoradiography. I, 20% of radiolabelled precursor protein used in each import reaction; The arrowhead marks an additional band of the size of the cleaved N-terminus of Mcp3.
Figure 8(A) Import of Mcp3 is mediated by the MIM complex. Mitochondria isolated from WT, mim1Δ, or mim2Δ cells were incubated with radiolabelled Mcp3 for the indicated time periods. After import mitochondria were reisolated and analysed by SDS-PAGE and autoradiography. Bands corresponding to the mature (m) form were quantified. Import after 15 min into wild-type mitochondria was set to 100%. The mean with standard deviations is depicted (n=3; SD). I, 20% of radiolabelled precursor protein used in each import reactionB) Steady state levels of over-expressed HA-Mcp3 are reduced in cells lacking MIM subunits. Crude mitochondria were obtained from WT cells containing an empty plasmid (Ø) and from wild-type, mim1Δ or mim2Δ cells containing a plasmid encoded HA-Mcp3. Samples were analysed by SDS-PAGE and immunodecoration with antibodies against the HA-tag, Tom20 as MIM substrate and Fis1 as a loading control. HA-Mcp3 levels were quantified in relation to Fis1 levels. Levels in wild-type cells were set to 100%. The bar diagram shows the mean with standard deviation (n=3; SD; *, p < 0.05; **, p < 0.01).(C) Mcp3 precursor binds in vitro to Mim1. Radiolabelled Mcp3 was incubated with amylose beads harbouring recombinant MBP or MBP fused to Mim1. After washing proteins were eluted with sample buffer. Analysis was performed by SDS-PAGE, blotting and autoradiography. To demonstrate equal amounts of MBP fusion proteins the membrane was stained with Ponceau S. I, input 5% of precursor used; n.b., 5% of unbound material;.b, 100% of bound material.