細胞の肋骨を壊すものが、細胞をより強くする

Home What Breaks a Cell’s Ribs Can Make It Stronger Comment Save Article Read Later Share Facebook Copied! Copy link Email Pocket Reddit Ycombinator Comment Comments Save Article Read Later Read Later biomechanics What Breaks a Cell’s Ribs Can Make It Stronger By Jake Buehler June 29, 2026 The mechanical process of cell division exerts powerful, if microscopic, forces. How do the molecular machines that power it manage the strain? Comment Save Article Read Later As the mitotic spindle tightens to separate chromosomes during cell division, it produces and absorbs forces. Ada Zejun Shen/Quanta Magazine Introduction The cells of animals, plants, and fungi start their lives by being torn apart. Cells are born by division, and just before a parent cell becomes two daughters, it doubles its nuclear DNA and carefully condenses it into X-shaped chromosomes. The nucleus disassembles, letting these crucial genetic instructions float free in the cell’s soupy interior. Then the cell performs an astounding, microscopic feat of strength. Proteinaceous cables extend from the cell’s poles toward the equator and latch onto the chromosomes. They drag, tilt, and nudge the precious cargo until every chromosome has been ushered into a tidy line around the cell’s middle. Then this spindle apparatus, as it’s known — a sinewy, dynamic rib cage made of bundles of microtubules — shortens itself at both poles. This wrenches the chromosomes apart into two sets and reels them to opposite ends of the cytoplasm sea. With its genetic material segregated at either pole, one cell can safely become two, born from a microscopic tug-of-war. The spindle strains against itself as it shortens and pulls; how it does this without ripping itself apart has been a scientific mystery since biophysicists first observed cell division with microscopes 150 years ago. “They saw them [the chromosomes] moving, which led to this idea that there’s probably forces that are pulling or pushing things around,” said Colleen Caldwell, a biophysicist at the University of Groningen. If absorbing those forces caused the spindle’s integrity to fail, it could spell the end for both daughter cells or cause diseases that arise from errors in cell division and chromosome arrangement. In this way, all eukaryotic life, including human life, rides on the spindle’s success with each cell division across an organism’s lifetime. Until recently, researchers didn’t have the tools to physically manipulate the mammalian spindle structure at the subcellular scale to toy with it and find out how it works. Recently a team of researchers led by Sophie Dumont, a biophysicist at the University of California, San Francisco, used microneedles to physically manipulate and stress the structure in mammal cells for the first time — and then observe how the spindle holds together through intense strain as it wrenches the chromosomes apart. The experiments have shown how a self-repair mechanism enables the spindle to stabilize itself under force and avoid disintegrating. These findings, which were published in February 2026 in Current Biology, provide a window into the physics of the cellular world, where complex living machines endure physical forces and stresses like machines in a factory. The spindle’s mechanical quirks show just how weird materials science can get at the finest scales of life. A Living Material By virtue of being biological, the cell spindle presents massive complexity for materials physicists. Most human-made materials contain just a few different types of molecules, said Colm Kelleher, a biophysicist at Syracuse University who was not involved with the new research. Meanwhile, the spindle is made of hundreds of different types of individual protein molecules, and any one of them is “an extremely complex object,” he said. That puts the spindle in an unusual size class that complicates experiments. “There’s quite a bit that scientists know about the mechanics of individual molecules, and there’s quite a bit that scientists know about the mechanics of tissues and organisms, like how muscles generate force,” Dumont said. “But mechanics at this scale of many molecules together forming this macromolecular structure is harder to probe. So we know less about it, but it’s just as important.” One last wrinkle is that, by being part of a living organism, these biomolecular structures are constantly consuming energy from within the materials themselves — very unlike how human-made materials and machines work. Kelleher gave the example of a car: It has a fuel tank and an engine, which power components that transfer torque to the wheels, which then push against the ground. A system made of biological materials works very differently. Mark Belan/Quanta Magazine “It would be like if you had a car where there were only wheels, and you injected the gasoline directly into the wheel, and it all started moving itself,” he said. “The force-generating components, the energy-consuming components, and the force-transferring components are all physically mixed up with each other.” Despite the mechanical oddities inherent to living machines, investigations into spindle physics have been going on for decades. In the 1960s, the late Duke University biologist Bruce Niklas started using extremely fine glass needles to probe and manipulate chromosomes in living cells by pushing from the outside against the cell membrane. By exerting physical force on the spindle and chromosomes, he and his colleagues revealed some of the key mechanics for the first time. For example, tension on the kinetochores — the disc-shaped proteins to which the spindle’s fibers attach on the chromosome — is thought to let the cell confirm the spindle’s correct attachment and ensure the proper separation of chromosomes during cell division. The stages of cell division. The cell spindle (green) attaches to the chromosomes at their kinetochores (pink). It lines them up in the middle of the cell and then pulls them apart to opposite poles. Then the cell splits into two. Wellcome Images/Science Source Over the next few decades, Niklas’ work prodding and pulling on the fibers started the field of spindle mechanics, Dumont said. He is “basically our hero,” she added. His work opened up questions about how the spindle generates force, how much force it can produce, and how it responds to any forces the environment exerts on it. However, his work was done in a very specific type of cell: grasshopper spermatocytes, the progenitors of grasshopper sperm cells. These cells had some experimental benefits. They tolerate physical manipulation with glass microneedles, for instance, and have large, easily observable chromosomes. But Dumont wanted to look beyond insects to find out know how the spindle behaves in mammalian cells like ours. She needed to find a type of mammal cell that, like Niklas’ grasshopper spermatocytes, had large but relatively few chromosomes and were amenable to manipulation by microneedles. The cells of rat kangaroos, rabbit-size nocturnal marsupials, have only 12 or 13 chromosomes depending on the sex. They turned out to be ideal. For approximately 10 years, Dumont’s lab has tugged on rat kangaroo cells with microneedles — “sometimes we call it cell torture,” she said — to see how they respond to different forces. A Spindle’s Resilience In 2020, her team got a surprise. When they yanked on the fiber with the microneedle, it did not detach from the chromosome or from the spindle’s anchor points at the cell’s poles. The fiber broke in the middle, like a pencil snapping in two. What’s more, the ragged ends of the busted fibers didn’t immediately unravel. They settled into a stable form, like a nylon rope whose frayed end has been melted to stop further disintegration. Caleb Rux, a bioengineer in the Dumont lab, looked more closely at how the fibers were breaking and somehow being stabilized afterward. To manipulate the spindle with extreme precision, he used what looked l