Biological complexity: cell molecular communication (Introduction)

by David Turell , Wednesday, January 27, 2016, 18:29 (3223 days ago) @ David Turell

Cells respond to molecular signals they are programmed to interpret:-http://www.sciencedaily.com/releases/2016/01/160121121825.htm-"To decide whether and where to move in the body, cells must read chemical signals in their environment. Individual cells do not act alone during this process, two new studies on mouse mammary tissue show. Instead, the cells make decisions collectively after exchanging information about the chemical messages they are receiving.
"Cells talk to nearby cells and compare notes before they make a move," says Ilya Nemenman, a theoretical biophysicist at Emory University and a co-author of both studies, published by the Proceedings of the National Academy of Sciences (PNAS). The co-authors also include scientists from Johns Hopkins, Yale and Purdue.-"The researchers discovered that the cell communication process works similarly to a message relay in the telephone game. "Each cell only talks to its neighbor," Nemenman explains. "A cell in position one only talks to a cell in position two. So position one needs to communicate with position two in order to get information from the cell in position three."-"And like the telephone game -- where a line of people whisper a message to the person next to them -- the original message starts to become distorted as it travels down the line.-"The researchers found that, for the cells in their experiments, the message begins to get garbled after passing through about four cells, by a factor of about three.-***-"Since at least the 1970s, and pivotal work by Howard Berg and Ed Purcell, scientists have been trying to understand in detail how cells decide to take an action based on chemical cues.-"Every cell in a body has the same genome but they can do different things and go in different directions because they measure different chemical signals in their environment. Those chemical signals are made up of molecules that randomly move around.-"'Cells can sense not just the precise concentration of a chemical signal, but concentration differences," Nemenman says. "That's very important because in order to know which direction to move, a cell has to know in which direction the concentration of the chemical signal is higher. Cells sense this gradient and it gives them a reference for the direction in which to move and grow."-***-"The clumps of cells, working collectively, could detect insanely small differences in concentration gradients -- such as 498 molecules of EGF versus 502 molecules -- on different sides of one cell," Nemenman says. "That accuracy is way better than the best possible margin of error determined by Berg and Purcell of about plus or minus 20. Even at these small concentration gradients, the organoids start reshaping and moving toward the higher concentration. These cells are not just optimal gradient detectors. They seem super optimal, defying the laws of nature."-***-"Together, the two papers offer a detailed model for collective cellular gradient sensing, verified by experiments in mouse mammary organoids. The collective model expands the classic Berg-Purcell results for the best accuracy of an individual cell, which stood for almost forty years. The new formula quantifies the additional advantages and limitations on the accuracy coming from the cells working collectively."-Comment: Note that the cells identify the type of signal and the strength of the signal. This study implies automaticity. Bacteria studied by Shapiro are on their own and must be more independent so I believe they are also automatic but have a greater variety of programmed esponses.