before coculture, cells were stained with mitotracker or pkh67 cell linker ( pkh67gl, sigma - aldrich ) and washed with pbs. for imaging, cells were cultured on glass coverslips in complete dmem and imaged using an axio imager m2 microscope equipped with an axiocam mr camera and zen 2 software or using an axioscan 7 microscope slide scanner equipped with a color axiocam 705 color complementary metal – oxide – semiconductor camera and a fluorescence axiocam 712 mono camera ( all from carl zeiss ). image processing and analysis were performed using fiji imagej ( https: / / imagej. net / fiji ) or qupath. for mechanistic studies, cocultures were treated with dih ydrocytochalasin b ( 100 nm ), nocodazole ( 10 μm ) or carbenoxolone ( 100 μm ) ( all from sigma - aldrich ) for 24 h. injection of mitochondria was performed using a fluidfm setup as previously described. imaging was carried out using a spinning disc confocal microscope ( visitron systems ) with a yokogawa csuw1 scan head and an electron - multiplying charge - coupled device camera system ( andor oxford instruments ). a total of 100, 000 fibroblasts were seeded in two - well microinsets 6 h before injection. the microfluidic probe was positioned over individual fibroblasts and mitochondria were inserted using a cantilever system. z stacks were taken to identify successful transfer of mitochondria. consequently, 100 fibroblasts were injected and fixed in 4 % paraformaldehyde ( pfa ) for 24 h after transfer and analyzed by immunoflu orescence staining. mitochondria were extracted from 20, 000, 000 epithelial cells using a mitochondria isolation kit ( 89874, thermo fisher scientific ). mitoception was performed as described using preseeded cells in six - well culture plates. a total of 100, 000 hpfs were seeded the day before mitoception. mitochondria isolated from 100, 000 cells of various cell lines or primary cells, which included similar amounts of total protein ( extended data figs. 4c and 6d ), were added to the bottom, ensuring even distribution. culture plates were centrifuged at 1, 500g for 15 min at 4 °c and incubated at 37 °c and 5 % co2 for 2 h. the centrifugation procedure was repeated and cells were cultured for 24 h before further processing. for oxphos inhibition, recipient fibroblasts were treated with 1 μm oligomycin ( o4876, sigma - aldrich ) for 24 h. all experiments were performed with consistent exposure time of cells to mitochondria, uniform mitochondrial uptake across experiments and standard post - transplantation conditions. data were normalized to the number of donor cells. cells were stained with sytox blue ( s34857, thermo fisher scientific ) before acquisition or analysis. live mitotracker - high and mitotracker - low cells or su9 – rfp - high and su9 – rfp - low cells were sorted using a facsaria fusion sorter ( bd biosciences ) with a 100 - μm nozzle and 20 psi pressure on the basis of their fluorescence intensity. the number of cells was normalized after each facs run. to analyze proliferation, cells were fixed and permeabilized using a foxp3 transcription factor staining buffer set ( 00 - 5523 - 00, ebioscience ) before intracellular staining with pe - conjugated ( sc - 7846, santa cruz ) or pe – cyanine7 - conjugated ( 25 - 5698 - 82, ebioscience ) anti-ki67 for 1 h at room temperature. for mitochondrial content analysis, cells were stained with mitotracker green fm ( m46750, thermo fisher scientific ). flow cytometry was performed using an lsr fortessa or a facsaria fusion cell analyzer ( both from bd biosciences ). data were analyzed using flowjo version 10. 10 software ( bd biosciences ). chemotactic transwell migration was assessed as described previously and cancer cells were allowed to migrate for 24 h toward cm from fibroblasts. transwell coculture assays were previously described. a total of 100, 000 cells per well were seeded on xf96 seahorse plates in full medium. the medium was then switched to seahorse xf base medium ( 103335 - 100, agilent technologies ) supplemented with 10 mmol l glucose, 1 mmol l sodium pyruvate and 2 mmol l glutamine ( assay concentration, https: / / www. agilent. com / cs / library / usermanuals / public / xf _ cell _ mito _ stress _ test _ kit _ user _ guide. pdf ) and incubated in a co2 - free incubator for 1 h. oligomycin, carbonyl cyanide - p - trifluoromethoxyphenylhydrazone ( fccp ) and antimycin a ( aa ) + rotenone were prepared in the xf assay medium with final concentrations of 1, 1. 5 and 1 / 0. 1 μmol l, respectively, and provided by the seahorse xf cell mito stress test kit ( 103015 - 100; agilent technologies ). the compounds were injected to assess the ocr of cells in an xf96 plate. metabolic flux data were normalized to cell count, which was determined using hoechst staining and analysis in a fluorescence reader ( agilent technologies, biotek cytation 1 ) on the day of analysis. atp levels were determined using the celltiter - glo assay kit ( promega ). mitochondrial ros were measured as previously described using mitosox - red ( m36008, thermo fisher scientific ). ecm was decellularized with 0. 5 % trit on x - 100 in 20 mm nh4oh for 1 – 3 min and washed with pbs before fixation with 4 % pfa for 15 min at room temperature. immunostaining was performed to analyze the expression of ecm proteins in the decm. hoechst staining was performed to assess the efficiency of decellularization. histological analyses and immunostainings were performed as described previously using the antibod ies listed in supplementary table 2. immunoflu orescence images were analyzed using fiji and staining intensity was normalized to cell number with at least nine microscopic fields of view for each condition analyzed. mitochondrial networks were analyzed with mina as previously described. the relative distance is indicated with values from 1 to 10; at least 100 – 200 intensity profiles were measured. colony area and decm area were measured after thresholding the images using imagej ( fiji ). colocalization analysis was adapted from delaunay et al.. fluorescent intensity profile on the specified line was measured using imagej ( fiji ) and normalized by the highest intensity value. all images from the same experiment were processed in an identical way by adjusting brightness and contrast and subtracting background signal to identify cell edge and contour or thresholding with the same values using a wide - field microscope. the length of tnts between cancer cells and fibroblasts was measured using the line or polygon tool in qupath. holotomographic imaging was performed with a tomocube ht - x1 microscope ( tomocube ). cells were seeded on glass - bottomed dishes ( p06 - 1. 5h - n, cellvis ) at a density of 1 × 10 cells per dish. the laser module was aligned for optimal illumination of the sample. the imaging process captured the cells ’ refractive index and immunoflu orescence labeling. videos were acquired using a high - speed camera for 6 h with a time interval of 5 min. finally, tomocube software was used to process the acquired images. rna isolation and rt – qpcr were performed as described previously using the primers listed in supplementary table 3. values obtained for the first control were set to 1. western blot analysis was performed using standard procedures and antibod ies to miro2 ( h00089941 - b01p, novus biologicals; 1: 1, 000 diluted ), miro1 ( nbp1 - 59021, novus biologicals; 1: 500 diluted ), trak1 ( pa5 - 70029, invitrogen; 1: 500 diluted ), trak2 ( pa5 - 21858, invitrogen; 1: 500 diluted ), exoc1 ( ab251853, abcam; 1: 500 diluted ), exoc2 ( ab140620, abcam; 1: 500 diluted ), vinculin ( v4505, sigma - aldrich; 1: 2, 000 diluted ), gapdh ( 5g4, hytest; 1: 10, 000 diluted ) and hsp60 ( ab59457, abcam, 1: 500 diluted ). secondary antibod ies were anti-rabbit or anti-mouse igg ( w4011 and w4021, promega; 1: 10, 000 diluted ) conjugated with horseradish peroxidase.