Scientists have found that typical cells in animals have the ability to transmit and receive biological signals by making physical contact with each other, even at long distance.
The finding directly contradicts the standard biological model of animal cell communication.
The newly discovered mechanism is similar to the way neurons communicate with other cells.
It goes against the standard understanding that non-neuronal cells "basically spit out signalling proteins into extracellular fluid and hope they find the right target," said senior study investigator Thomas B Kornberg, a professor of biochemistry with the University of California - San Francisco Cardiovascular Research Institute.
Working with living tissue from Drosophila - fruit flies - Kornberg and his team demonstrated that cells send out long, thin tubes of cytoplasm called cytonemes, which Kornberg said "can extend across the length of 50 or 100 cells" before touching the cells they are targeting.
The point of contact between a cytoneme and its target cell acts as a communications bridge between the two cells.
"It's long been known that neurons communicate in a similar way - by transferring signals at points of contact called synapses, and transmitting the response over long distances in long tubes called axons," said Kornberg.
"However, it's always been thought that this mode of signalling was unique to neurons.
"We have now shown that many types of animal cells have the same ability to reach out and synapse with one another in order to communicate, using signalling proteins as units of information instead of the neurotransmitters and electrical impulses that neurons use," he said.
"I would argue that the only strong experimental data that exists today for a mechanism by which these signalling proteins move from one cell to another is at these points of contact and via cytonemes.
"There are 100 years worth of work and thousands of scientific papers in which it has been simply assumed that these proteins move from one cell to another by moving through extracellular fluid.
"So this is a fundamentally different way of considering how signalling goes on in tissues," Kornberg said.
Working with cells in the Drosophila wing that produce and send the signalling protein Decapentaplegic (Dpp), researchers showed that Dpp transfers between cells at the sites where cytonemes form a connection, and that cytonemes are the conduits that move Dpp from cell to cell.
The scientists discovered that the sites of contact have characteristics of synapses formed by neurons. They demonstrated that in flies that had been genetically engineered to lack synapse-making proteins, cells are unable to form synapses or signal successfully.
"In the mutants, the signals that are normally taken up by target cells are not taken up, and signalling is prevented. This demonstrates that physical contact is required for signal transfer, signal uptake and signalling," said Kornberg.
