Working with cells in the Drosophila wing that produce and send the signaling protein Decapentaplegic (Dpp), Kornberg and his team 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 signaling is prevented," said Kornberg. "This demonstrates that physical contact is required for signal transfer, signal uptake and signaling."
Kornberg said that a major reason that animal cell cytonemes had not been observed or studied previously is because these structures are too fragile to survive traditional laboratory methods of preparing cells for imaging. "During the last decade or so, though, there have been fantastic technical advances, including new techniques in genetic engineering, new microscopes that improve the resolution and sensitivity for imaging living cells and the development of fluorescent marker proteins that we can attach to proteins of interest."
Using these new technologies, Kornberg and his team have captured vivid images, and even movies, of fluorescent signaling proteins moving through fluorescently marked cytonemes.
"We are not saying that cells always use cytonemes for signaling," Kornberg cautioned. "Hormones, for example, are another method of long distance cell si
|Contact: Peter Farley|
University of California - San Francisco