Using specialized imaging techniques and customized microscopes to watch single embryonic chick cells in real time, scientists at
"The presence of these structures...was really unexpected," said Maria Barna, an assistant professor of developmental biology and genetics at Stanford, in a statement. Barna is senior author of a study describing the discovery, published online Sunday by the journal Nature.
Scientists have long thought that cells send and receive so-called signaling molecules -- chemical messages directing how they develop and behave -- through a process of diffusion, where one cell sends a signal into the medium around it, and the signal then floats along to another cell.
Cells may indeed communicate in this manner, the researchers noted. But the new images suggest that in some cases, embryonic cells develop long, thin extensions that can reach "several cell diameters away," stretching and contracting until they make contact with a separate, target cell, Barna said. The signals travel through that connection.
When the researchers applied a fluorescent chemical tag to a particular signaling molecule they wanted to study in chick cells -- the wonderfully named sonic hedgehog protein, which helps direct embryonic development -- they were able to watch the molecule move down one of the newly discovered extensions of one cell and over to a corresponding extension on another cell. (Read this to learn how sonic hedgehog got its name.)
Barna said she and her colleagues will now investigate what other types of cells use filopodia as well, and for what purposes. "We are really just scratching the surface of what we can learn," she said.
In this clip, it's possible to see the filopodia (as the structures are called) of one chick cell, colored green, reach out and make contact with the filopodia of another cell, which are colored red.