The butterfly effect in ER dynamics and ER-mitochondrial contacts

• For the first type, evidence of the chaotic behavior of ER dynamics is reported.
• The discovery of chaos in the ER network is significant for studying bio-dynamics.
• Experimental results can be better interpreted when taken chaos into account.

The endoplasmic reticulum (ER) is a major organelle of cells in eukaryotic organisms. The ER that is a polygonal network consisting of tubules and sheets has been known to be extremely dynamic in animal cells. However, understanding about the mechanism underlying ER-network motions is rarely explored. Discovering the type of dynamics that governs the movements of the ER network is essential for gaining insights into the structure and functions of cells. For the first time, this paper shows the evidence of chaotic behavior in the dynamics of the ER network and ER-mitochondrial contacts which were captured by time-lapse microscopy images. The chaotic properties of ER-network dynamics and ER-mitochondrial interactions were quantified using the largest Lyapunov exponent and fractal analysis. The results also suggest that the degree of chaos in ER dynamics reduces after drug treatment. New knowledge about the nonlinear dynamics that gives rise to the complex behavior of the organelles will lead to a new perspective of experimental design, and addressing questions relating to their functions and regulations.