Calcium signals at cytoneme contacts amplify Wnt/β-catenin signalling
This study demonstrates that focal calcium transients at cytoneme contact sites stabilize cell-cell adhesion via E-cadherin in a positive feedback loop with Wnt signaling, thereby facilitating efficient ligand transfer and amplifying canonical Wnt/β-catenin pathway activation.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Cells in our bodies are constantly talking to one another, sending chemical messages that tell them when to grow, when to move, and how to organize themselves into tissues. One of the most important messengers in this conversation is a protein called Wnt. Because Wnt is greasy and sticky, it cannot simply float through the watery spaces between cells like a scent drifting on the wind. Instead, it needs a delivery vehicle. Scientists have discovered that cells grow thin, finger-like extensions called cytonemes to reach out and touch their neighbors, acting as direct pipelines to pass these messages. However, a major mystery remained: when a cytoneme touches another cell, how does the receiving cell know this is a real message and not just a fleeting, accidental brush? Without a way to verify the contact, the signal might be lost before it can do any work.
Researchers at the University of Exeter have now uncovered a crucial step in this process. They found that when a cytoneme carrying a Wnt message touches a receiving cell, it triggers a tiny, rapid flash of calcium right at the point of contact. This flash acts like a security check, confirming that the connection is real. Once this calcium signal fires, it helps lock the two cells together more firmly, allowing the Wnt message to be transferred efficiently and turn on the genes needed for growth and development. The team showed that without this calcium flash, the contact remains weak and the message fails to get through.
To see this happening, the scientists used human cells grown in a lab dish, which are excellent for watching these tiny structures in action. They observed that these cells send out long, thin filaments that carry the Wnt protein and the machinery needed to receive it. When these filaments touched a neighboring cell, the researchers saw a sudden, localized spike in calcium levels exactly where the two membranes met. This was not a random event; it happened specifically when the Wnt-carrying filament made contact. The researchers found that if they blocked the calcium from entering the cell, the contact between the two cells became unstable and broke apart quickly. Conversely, when they boosted the calcium levels, the cells held on to each other for much longer, giving the Wnt signal plenty of time to cross over.
The study revealed that this calcium flash does more than just hold the cells together; it actively recruits a sticky protein called E-cadherin to the contact site. This protein acts like a molecular glue, reinforcing the connection between the two cells. The researchers discovered that the presence of Wnt and the calcium flash work together to bring this glue to the junction. When the glue is present, the cells form a stable bridge, and the receiving cell successfully gathers the Wnt signal into a complex that travels to its nucleus to switch on specific genes. The team confirmed this by showing that when they increased the amount of E-cadherin in the cells, the contact stability improved, leading to a significant boost in the Wnt signal reaching the nucleus.
This discovery changes how we understand the relationship between two major branches of cell signaling. For a long time, scientists believed that the calcium pathway and the Wnt growth pathway worked against each other, with one turning the other off. This new work suggests that at the very moment of contact, they actually work together. The calcium signal does not shut down the growth message; instead, it authenticates it. It ensures that only stable, verified connections trigger the growth program. This mechanism prevents cells from reacting to every random touch, ensuring that they only respond to genuine, sustained signals from their neighbors.
The researchers confirmed these findings by manipulating the levels of calcium and Wnt in the cells. They found that adding extra Wnt protein increased the strength of the calcium flashes at the contact points. They also showed that when they increased the levels of the sticky E-cadherin protein alongside Wnt, the cells held on to each other more effectively, resulting in a much stronger Wnt signal in the receiving cells. This proves that the calcium flash is the trigger, and the sticky protein is the necessary tool that makes the connection last. The team concluded that this process acts as a gatekeeper, converting a brief, exploratory touch into a lasting, productive conversation between cells.
By mapping out this sequence of events, the study provides a clear picture of how cells distinguish between noise and a real message. It shows that the physical act of touching is not enough on its own; the cell must also generate a specific chemical response to validate the contact. This local calcium signal serves as a confirmation code, ensuring that the complex machinery required for growth is only assembled when a reliable connection has been established. This level of control is likely essential for building healthy tissues and preventing errors that could lead to disease, offering a new understanding of the precise rules that govern how cells build the body.
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