I want to know if there is any noise in the estimation of a cell (especially cancer cell) about number and type of neighbor cells. I also want to know what factors are involved in the amount of noise? Does the phenotypic behavior of cells (i.e., being quiscent, prolifertive, apoptotic, and necrotic) influence the amount of noise?
Noise is ubiquitous in gene expression, and therefore, has implications for phenotypic variation.
Dear Negin
When normal cells are cultured in a Petri dish, initially they get into proliferative phase. But once the number grows to a value where the surface is filled up (the outer cells touch the walls of the dish), they stop growing and become quiscent, depending on cell loss factor. This is because of 'noise-less' inter cellular communication. Now cancer cells either do not 'listen' to surrounding cells, or they lack ears for this, or very likely all the neighbouring cells 'speak' different languages, it is all just noise for them (imagine a colony where all individuals speak different languages; everything is just gibberish or noise'). So they just dont stop; it is free for all and each one to itself. So they do not stop growing, remain proliferatng and there is no contact inhibition and they pile up in the dish. So, you can very well say that there is noise in the dish (like a storm in the tea pot)
Now noise in the other sense. Any chemical reaction is a mini explosion, accompanied by microscopic or sub-microscopic light and sound. Light has been demonstrated inside cells; actually generation of heat energy is the aim of body cell metabolism. I don't think sound has been; we may be lacking instruments to measure such low intensity sounds
Narayanan
Noise is an "observable". The dilemma with this question is that noise is not defined so the question is impossible to answer appropriately. Is this "noise" really sound waves Narayanan thinks? or is this "noise" aberrant " polarization of membrane, measurement of background gene expression or such? To a chemist, noise defines the threshold that must be crossed for an observable such as a peak to be detected.
Dear Peter and Narayanan:
If a cell can't obtain the exact information of its neighbors, I call it noise. For example, if there are five cells in the neighborhood of a cell, but the cell can recognize just three of them, there is a noise in cell communication. I want to know more if there are such noises in cell communication.
Let me now assume that you are talking about a sheet of epithelial cells. Since these cells are polarized, they can define an up or down ( arbitrary directions) every neighboring cell will have contact points with the cell. The contact points have gap junctions and many other adherins which send signals to and from the cell to neighbors. This allows for them to act as a unit when needed.
Now in a dish, the epithelial cells loose the ability to polarize when kept alone but will polarize when they make lots of cell cell contacts. These cell cell contacts send lots of signals and the signals can effect the differentiation state, proliferative ability and motility of a cell. Many biologist will refer to the state of change of cells moving from sparse to dense conditions as contact inhibition because it is how growth factors are inhibited. On the other hand, hepatocytes when placed in spares culture loose the ability to properly make numerous p450s. So a sparse culture of heptocytes is worthless for ADMET experiments. With the exception of nerves most other cells in the body make extensive connections to their neighbors and send real signals not noise that will have distinct effects. Is your observable one of the effects? Only experimentation will determine this.
Dear Negin and Peter
In the first part of my answer, I dealt with noise as aberrant communications; cancer cells produce noise. In the second part I dealt it as sound waves. I did that because I was not sure what Negin meant, and both are applicable
Narayanan
Dear Colleagues
Apart form the question how to define noise, I would like to add one more component that contributes to noise: electromagnetic waves. They are emitted in different frequencies (depending also on cell numbers ...) and there is evidence that malign cells have in comparison to healthy cells different emission patterns.
(more about this topic in: Fields of the Cell; eds. Fels, Cifra, Scholkmann; Research Signpost; open access).
Daniel
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