Rebuilding a body from scratch is a daunting task that requires careful coordination between everyone involved. That is why the beginnings of nature – cells – have learned to be remarkably talkative in order to do the job properly.
Decades of experiments with fish, frog, and mouse embryos have given a general picture of how these cellular conversations often go. Cells send out molecular signals that can diffuse deep into their surroundings, similar to messages that are sent via radio waves. Such widespread messages that relay information to distant anatomical locations have long been considered essential to building a body.
But nature has also developed more subtle methods of sending messages.
Dr. Guignard and his colleagues may have overheard the sea splash embryos, sack-like filter feeders that inhabit the world’s shallow seabed, and may have found another way in which germinating cells correspond. In the earliest days, sea spray cells seem to only exchange signals with their closest neighbors, rather than sending signals to more distant cells, according to a paper published in Science on Thursday.
It is the microscopic equivalent of sharing notes between close friends – a conversation tactic whose range may be more limited than that of its long range counterpart, but which could allow the delivery of particularly precise instructions.
Most developmental biologists “never really thought about cell signals this way,” said Chen Cao, who researched the development of sea splashes at Princeton University, but was not involved in the new study. “This is a brand new perspective” on how embryo cells find their fate, she said.
Sea splashes are more closely related to vertebrates – animals like people with backbones – than you can expect from brainless blobs. And the embryos of some sea spray species like Phallusia mammillata, are completely transparent and therefore particularly easy to observe.
The researchers used a highly sensitive form of microscopy to track 10 Phallusia mammillata embryos during six hours of their early development. The cameras took pictures every two minutes and recorded the position and shape of each cell in the embryo through several rounds of division until the future sea contained several hundred cells each, about a third of the way of development.
In contrast to frog or mouse embryo cells, which can move back and forth during development, young sea spray cells mostly remained in place. Mathematical modeling also showed that the cells only signaled to the cells they touched, almost as if they were whispering to each other. At least in these early stages of development, sea spray cells did not seem to need a long distance call.
The results suggest that “you can be a whole sophisticated embryo using local signals alone,” said Patrick Lemaire, developmental biologist at the University of Montpellier in France and co-author of the study.
Remarkably, these patterns were repeated in all the sea splashes observed by the team to the point where the same cells occupied almost identical neighborhoods in different embryos. Dr. Lemaire said he believed this rigid consistency could have played a role in keeping the mushy forms of sea splashes largely unchanged since they appeared on the planet hundreds of millions of years ago.
“This is a nice job,” said Cassandra Extavour, a development biologist at Harvard University who was not involved in the study. And although sea splashes are the only creatures where these development patterns have so far been strictly documented, Dr. Extavor believes that “there will be many more animals based on a signaling principle like the one described here.”
Different types of signaling are also not mutually exclusive. Dr. Cao said she thinks even sea spray booths could make some long-distance calls later in development.
Scientists have long sought a unified view of how cell-cell communication between animals works, said Didem Sarikaya, a developmental biologist at the University of California at Davis, who was not involved in the study. But it is becoming increasingly clear that this is not the case, said Dr. Sarikaya.
“We tend to watch the things we knew about before,” said Dr. Extavor. But “if we understand that this lens is very narrow, we may not be surprised by such results.”