World’s first success in reproducing rotational cytoplasmic flow with artificial cells

New possibility for designing nutrient delivery system with higher efficiency, modeled after living organisms

Waseda University researchers became the first in the world to successfully reproduce rotational cytoplasmic streaming by microtubule networks with artificial cells. They also discovered that microtubule networks use, in addition to hydrodynamic interaction, mechanical interaction and the physical boundary to induce cytoplasmic flow over larger length scale and timescale.

This research is published in the American scientific journal, Proceedings of the National Academy of Sciences.


Directional stability and mechanism of rotational cytoplasmic flow. (A) Schematic illustration showing the mechanism of the rotational flow. (B) Time projection of the beads (Left) and ⟨ω⟩x (Right) with 50 nM Taxol. The lines and their surrounding areas represent means ± SDs, respectively. (Scale bar, 30 μm.) (C) Distributions of stable rotational flow (blue), unstable rotational flow (the flow changing its direction oppositely at least once per 30 min; red), and no rotational flow (⟨ω⟩x,t < 0.1 deg⋅min−1; gray; Movie S9) at various droplet diameters. Each bar includes 10–44 droplets.

Cytoplasmic streaming is the flow of cytoplasm, a liquid within a cell, and it is thought to be necessary for long-distance transport of micrometer-sized components, such as organelles and nutrients. There are two types of fibrous proteins that induce cytoplasmic streaming: actin filaments and microtubules. Although actin-based cytoplasmic streaming has been extensively studied, how microtubule bundles drive cytoplasmic flow in cells remained unclear. For example, in motor-driven elongation of microtubule bundles generated in oocyte (or, egg cells) of sea urchins and flies from the Drosophilidae family, the microtubule networks were known to form a rotating spiral structure, inducing the rotational cytoplasmic flow. Yet, conventional research on cytoplasmic flow rarely considered the mechanical nature of cell membranes and microtubules.

To better understand cytoplasmic streaming, this research focused on the role of cell membranes acting as a physical boundary, or a “wall.” When holding the end of a stick and pushing the other end onto a wall, the stick can bend or flex. The research team revealed that something similar happens between microtubule bundles and cell membranes, leading to the formation of a spiral-pattern organization of microtubules and the generation of a rotating vortex flow. This finding provides new point of view to research on cytoplasmic streaming, and it is expected to help unravel its mechanism.

Furthermore, biological systems are known to function with extremely high energy efficiency compared to man-made devices. Therefore, much research is now being undertaken with aims to structure systems modeled after the functions of living organisms. The results of this research make it possible to structure a transport system modeled after living organisms to deliver essential substances through the cell, contributing the fields of biology, medicine, and biomedical engineering.


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