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I've recently heard about experiments with brain tissue, where a virus is introduced in a rats brain, causing a "glow when electric charge is present" protein to be created. This protein then helps to study the brain using optical techniques to detect this glow. As far as I understand, not all cells in the brain were affected by this virus.

It seems like this kind of "virus operation" on DNA is pretty powerful, so my question is : at which point in an organism's life can a virus operation be done in such a way as to affect the entire organism for the rest of its life?

In other words, will a virus is introduced into a young embryo(or sperm), affect all cells and stay with an organism until death? Can it be introduced later and still have "complete effect"?

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Note that in the type of experiments you are referring to (for instance look for "in vivo optogenetics") you generally do NOT want to infect all of the neurons in the brain, but rather a very specific subpopulation. This is achieved by using various strategies, which essentially depend on the presence of specific DNA sequences in the virus or in the target neurons. Also, if you do this in adult animals, the virus will only infect cells around the site at which it has been injected. –  nico Aug 29 '13 at 11:45
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The answer depends on two factors:

  • The type of vector (virus) you are using
  • How well your vector can be integrated.

The bottom-line is that there is no guarantee the vector will work even if you start from the embyro.

As far as I know, the problem of using vectors in general is that the vector you are using might not be integrated into the genome of the host. (Not necessarily get into the DNA, but just keep replicating during each S phase.) Therefore doing it earlier gives you a better chance to actually get them in the organism.

For example, there is a linear vector used in C. elegans that was injected into the oocyte even before fertilization. The cell later treats the vectors as broken DNAs and linages them so they could be pull to one side of the cell during mitosis. However, the huge chunk of vector DNA is mosaic. (i.e. only some of the cells in that worm have the vectors.) Other vectors like engineered HIV have better chance to integrate themselves.

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