A team of scientists from Technische Universität Dresden has uncovered a surprising new mechanism for how large embryonic cells divide. This discovery challenges the long-held belief that a fully closed contractile ring is essential for cell division. The researchers, studying zebrafish embryos, found that instead of a complete actin ring, these cells use a 'mechanical ratchet' system to divide. This system relies on microtubules and the physical properties of the cytoplasm, which change in stiffness throughout the cell cycle. The researchers observed that the actin band remains stable as it contracts due to the stabilizing role of microtubules. When the cell enters interphase, the cytoplasm becomes stiffer, helping stabilize the actin band, allowing it to contract step by step. This process repeats across several cell cycles, gradually dividing the cell. This new mechanism may explain how large yolk-rich cells in animals like zebrafish and other species divide rapidly, providing a solution for those that cannot rely on traditional methods of cell division.