Fig. 7

Crosstalk between mitochondria and the eukaryotic host using heat flux as a biophysical signal. a Application of molecular thermometers reveals internal temperature of developing chicken midbrain (HH stage 9–10) at single cell level. Electron micrographs show erythroblasts inside the blood vessels (left) and subsequent to cannibalisation (right). Top scale bars (from left to right in µm): [8, 10, 20, 30, 40], bottom scale bars (from left to right in µm) [4, 1.5, 15, 10]. b Micro-thermographic visualisation of cycling cells using molecular beacons (MB-4: m4, MB-5: m5) after addition of heme⁻ and heme⁺ growth medium to the cells (T1: 1 h, T2: 2 h after adding the medium). Reduced intensity of MB-5 from T1 to T2 could potentially be a consequence of inhibition of OXPHOS via generated ATP, depletion/saturation of intermediate metabolites of TCA cycle, or heat-dependent denaturation of unstable cytochrome c. Scale bar: 5 µm. c Temperature-dependent intensity of fluorescence signal (y-axis) in PBS, cell lysate, and heme/PBS as per methods. While cell lysate and heme reduce the intensity of signal, sensitivity of the molecular beacons and overall kinetics of temperature-dependent activation remain unaffected. The reduced intensity of MB in cell lysate results from absorption of thermal energy by various proteins, and nucleic acids. Further, the emitted photons can potentially be absorbed by various proteins (including heme-proteins). In heme-treated samples, the reported capacity of heme to harvest the emitted light photons reduces the intensity of MBs. d Electron micrographs (right) show perinuclear localisation of mitochondria separated from the rest of cytoplasm by an intermediate zone occupied by dilated endoplasmic reticulum. The active mitochondria with enhanced membrane potential (top left; Mito.: MitoTracker red, control heme⁻ samples: Additional file 1: Fig. S2) increase the perinuclear and nuclear temperature (bottom left). The slight variability in the intensity of molecular beacon reflects variability of electroporation. Top scale bars (from left to right in µm): [3, 1, 0.2], bottom scale bars (from left to right in µm): [1, 3]