Between five and ten hours after a zebrafish egg is fertilized, something remarkable happens: a sheet of cells begins to move in a coordinated wave across the yolk in a process so elegant it resembles pulling a cap down over your head. Now, researchers at the Institute of Science and Technology Austria have revealed that this orchestrated movement—critical to all animal development—depends entirely on a single protein: keratin.
The discovery, published in Nature Communications by the Heisenberg group and Edouard Hannezo at ISTA, alongside colleagues from Sorbonne Université and Leiden University, illuminates why this structural protein, famous for its role in hair, nails, and horns, is so fundamentally necessary for life itself. During the earliest stages of embryonic development, a phase called gastrulation, cells reorganize and form the three germ layers from which all tissues and organs eventually arise. For decades, scientists understood that this process was critical—developmental biologist Lewis Wolpert famously argued it was the most important event in life—but the precise mechanics remained mysterious.
Suyash Naik, a researcher at ISTA, chose zebrafish embryos to crack this puzzle. At roughly one and a half hours old, zebrafish embryos are transparent spheres just millimeters across, floating in a petri dish of water. Unlike fruit flies commonly used in research, zebrafish are vertebrates with spinal cords similar to humans, making their developmental insights directly relevant to mammalian biology. More practically, their transparency allows scientists to observe development from the moment of fertilization—a window no other model organism offers so clearly.
The process Naik studied, called epiboly, is where the real action unfolds. A newly formed sheet of cells spreads down and around the yolk like an elastic cap, driven by forces within a thin network of yolk cells called the yolk syncytial layer. This cellular sheet continues spreading until it completely encloses the embryo in a protective layer, while inside, the first body layers begin to take shape. The entire choreography happens quickly, yet remains observable in detail under a microscope.
Inside each cell, keratin forms filaments that resemble tiny, curled noodles. Together with actin and myosin filaments, these structures make up the cytoskeleton—the internal scaffolding that gives cells their shape and strength. As epiboly begins, keratin activity ramps up and continues increasing throughout the process. But what makes keratin so essential? The researchers discovered that keratin acts as a "softener," modulating the mechanical forces that drive cell movement while simultaneously giving the cellular tissue the strength it needs to move together as a coherent unit.
Without keratin, this delicate balance collapses. Cells cannot maintain their coordinated movement, and the entire gastrulation process fails—which means embryonic development cannot proceed. The protein that we know best as the hardening ingredient in shampoo bottles turns out to be the hidden choreographer of one of life's most pivotal moments.
The findings reshape how scientists understand both development and the fundamental mechanics of cells in motion. As Naik's work demonstrates, sometimes the most essential proteins work in plain sight, hiding their importance in structures we see every day.