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Jun 03 2025
5Symmetry is a hallmark of most multicellular organisms, yet during embryonic development, cells divide asymmetrically. A team led by Prof. Dr. Esther Zanin at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) has now formulated a working model that clarifies how the protein anillin governs this asymmetry during the constriction of a dividing embryonic cell. Since anillin is found in large quantities in cancer cells, this insight might pave the way for innovative cancer therapies. Their findings have been published in the Journal of Cell Biology.
Under a traditional optical microscope, cell division can be observed in real time. At the outset, a ring composed of actin filaments forms around the middle of the parent cell, constricting evenly. However, as division progresses, the ring begins to contract more strongly at one side than the other, shrinking until the parent cell splits into two daughter cells.
Until now, the trigger for this asymmetry was unknown. Scientists understood that the process involved mechanical flows within actin fibers and the presence of anillin, but without anillin, the ring contracts symmetrically.
In Prof. Zanin’s laboratory, researchers study the first cell division in embryos of the nematode Caenorhabditis elegans. These cells measure approximately 0.05 millimeters in length and 0.02 millimeters in width, making them difficult to visualize in detail with conventional microscopy. To overcome this, scientists tag parts of the contractile ring with fluorescent proteins, allowing molecular-level observations via fluorescence microscopy. Mikhail Lebedev, the study’s lead author, engineered mutations in the anillin protein (which consists of 1,159 amino acids) by altering its docking sites. The team captured images of cell division every 15 seconds for each anillin variant to track how the ring constricted.
Their research identified two crucial regions on the anillin molecule that influence asymmetry: a compact, spherical (globular) domain and a highly flexible, unfolded region made of amino acid chains.
The contractile ring tightens as actin fibers slide past one another, powered by the motor protein myosin. Myosin activation depends on the switching protein RhoA, which toggles between an active form that triggers myosin and an inactive form that does not.
The breakthrough finding from Prof. Zanin’s team is that anillin doesn’t change the switching behavior of RhoA but instead makes the active form of RhoA inaccessible. When anillin’s globular domain binds to active RhoA, it blocks other proteins from attaching, preventing myosin from activating. This inhibitory effect is enhanced by anillin’s flexible region, which appears to “sense” mechanical flows in the actin fibers and modulate the globular domain’s binding ability.
Strong mechanical currents weaken the bond between anillin’s globular domain and RhoA, keeping the switch “on” and allowing myosin to contract the ring more forcefully at that location. This creates the asymmetrical constriction. Conversely, weak currents strengthen this bond, slowing contraction. The speed of actin fiber flow thus plays a critical role in determining the ring’s asymmetry.
How exactly the flexible region detects these currents and communicates with the globular domain remains a question for future research.
Because asymmetric constriction is observed not only in nematodes but also in human skin cells—reflecting the common evolutionary origin of all animals—these findings may deepen our understanding of skin’s protective functions and mechanisms that control tumor cell behavior.
This research opens exciting new avenues in cell biology and cancer treatment strategies by revealing the intricate molecular choreography behind asymmetric cell division.
Source:https://phys.org/news/2025-06-reveals-protein-anillin-asymmetry-embryonic.html
This is non-financial/medical advice and made using AI so could be wrong.
