Primordial chaos
Embryonic cells guess at genetic noise
Kirill Stasevich, "Science and Life"
Although we say that embryonic cells have no concern other than constantly dividing, and they also have no specialization, yet they differ from each other. And the differences between them appear already at the earliest stages of embryonic development.
In the future, different types of embryonic stem cells will give rise to tissues and organs: epithelium, blood, brain with its countless neurons, etc. – all this will happen by cellular standards for a long time, and the path of specialization will be very long, but it begins, again, very, very early. Even before the embryo is implanted into the uterine wall, its cells already have time to divide into two varieties, and then the embryo only does what it grows and differentiates: its different parts acquire characteristic features, functions, etc.
It is clear that when a cell wants to become different from its neighbors, it changes the activity of genes. Different genes are needed for different functions, so that cells performing the same role will be similar in genetic activity: they will have approximately the same genes working, and other genes, on the contrary, the cells will turn off.
Hisham Mohammed and his colleagues from the Babraham Institute in Cambridge found that when embryonic cells decide who they should be, it does not mean that they turn off the same genes together and turn on others. On the contrary, before the next stage of differentiation, cells turn on and off whatever they get, choosing from the genetic noise what is needed and what is not needed. And there is no correspondence in genetic activity between cells here; choosing their fate, they "make noise" inconsistently, turning on and off genes individually, without looking back at their neighbors.
This was found out using the methods of individual RNA sequencing: as you know, the activity of genes can be estimated by the number of RNA messenger molecules that are synthesized on DNA, and now we can analyze the composition of such RNAs in a single cell. And so the diversity of RNA clearly demonstrated the apparent disorder that reigns in the molecular kitchen of the embryonic cell before the next step in its specialization.
Having switched on and off its genes, the cell eventually understands what it needs in later life, and subsequently, when the choice is made, cells of the same fate behave the same way in genetic terms. However, as the authors of the work emphasize in their article in Cell Reports, in order for a cell to go one way or another, at the beginning it needs just such a noise. (It should be clarified here that the researchers were engaged in the very first events of cellular differentiation, and, perhaps, at later stages of embryonic development, everything goes without "guessing by genes".)
Of course, genetic noise should have its own molecular regulators that trigger all this violent molecular activity, but more detailed details here will become clear only after the following experiments.
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28.08.2017