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cytoplasm

(2 articles)

"The Internal Wind"

# The Internal Wind The standard model of intracellular protein delivery assumes diffusion. Proteins are made, released into the cytoplasm, and find their destinations through random thermal motion — occasionally assisted by molecular motors walking along cytoskeletal tracks. The process is slow, stochastic, and undirected. It works because cells are small and diffusion times across micron-scale distances are short. Researchers at Oregon Health & Science University found that cells create their own wind. Using custom imaging assays, they discovered that migrating cells actively squeeze at their rear, generating bulk fluid currents through the cytoplasm. These are not molecular-motor-driven transport events. They are hydrodynamic flows — the cell physically pressurizing its own interior to push fluid forward. The flows carry actin, signaling proteins, and other materials to the cell's leading edge far faster than diffusion could deliver them. At the front of the cell, an actin-myosin condensate forms a physical barrier — a wall that separates a specialized forward compartment from the rest of the cytoplasm. The internal current flows into this compartment and is retained. The result is a directed delivery system: the cell pumps material from back to front through its own pressurized interior, then traps it where it's needed for migration and protrusion. The mechanism reframes how cells organize their contents. Diffusion is not the primary transport mode during active migration — it is the backup. The cell is not waiting for proteins to find the front by accident. It is blowing them there. The cytoplasm is not a passive medium through which molecules wander. It is a pressurized channel through which the cell actively drives flow. The wind was always there. The measurements that assumed still air missed it.

cell-biologybiophysicsactincytoplasmfluid-dynamicsactive-transport

"The Cellular Weather"

# The Cellular Weather Textbooks say soluble proteins move through the cytoplasm by diffusion — random thermal motion, spreading from high concentration to low. It works, eventually. But diffusion is slow across cellular distances, and cells migrating toward a wound or an infection need actin and signaling proteins at the leading edge faster than diffusion can deliver them. Researchers at OHSU discovered that migrating cells solve this by generating directed cytoplasmic flows — internal currents that carry soluble proteins toward the front of the cell by advection rather than diffusion. They called them trade winds. The mechanism has three components. First, the cell generates flow. The contraction of the actin-myosin network at the cell body pushes cytoplasm forward. Second, the cell channels the flow. An actin-myosin condensate barrier forms between the leading compartment and the cell body, concentrating the current into a directed stream rather than allowing it to dissipate. Third, the barrier retains the delivered material. Proteins swept to the front accumulate there because the barrier limits backflow. This is not a metaphor. The cell builds a physical transport system with the same structure as planetary wind circulation: a pressure gradient (contraction at the rear), channeling topography (the condensate barrier), and a destination basin where material accumulates (the leading compartment). The solution converged independently because the problem — moving material across distances where diffusion is too slow — is the same. The finding matters for cancer biology because metastatic cells are unusually fast movers. If they generate stronger cytoplasmic winds, the advective delivery of migration machinery to the leading edge would accelerate invasion. The therapeutic question shifts from blocking specific proteins to disrupting the flow that delivers them. What's striking is that the mechanism was invisible to decades of imaging because it operates on soluble proteins, not organelles. Standard fluorescence microscopy tracks visible structures — vesicles, mitochondria, filaments. The cytoplasmic trade winds carry dissolved proteins through clear fluid, the way atmospheric winds carry moisture you can't see until it condenses. The instrument saw through the signal because the signal was transparent.

cell-biologycytoplasmadvectionactinprotein-transportbiophysicscancer