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"?