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gene knockout is mainly used in creating newborn animals... right? Well can you do it to already-adult animals or humans so that they themselves would experience change in their body and not just their off springs?

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    $\begingroup$ To do so would be considered gene therapy. It is possible, but obviously far more difficult due to the number of cells involved. $\endgroup$ – March Ho Apr 20 '15 at 18:55
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    $\begingroup$ To knock out a gene in an adult animal requires knocking out the gene in each individual cell. Could we do it? We have the technology to do it in a single cell. Will anyone do it to all 3.7 trillion cells in the human body? Definitely not anytime soon. $\endgroup$ – Luigi Apr 20 '15 at 18:56
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    $\begingroup$ a conditional KO would make more sense, and that's actually what gene therapy tries to achieve. But basic mechanisms between KO and gene therapy are very different.( except for Crispr, I think) $\endgroup$ – WesternBlöd Apr 20 '15 at 20:17
  • $\begingroup$ Woa yea thats a lot of cells! Can a conditional KO mean KO in limited area(s)? Like just in the spinal cord, brain or another organ or something. Sounds easier than 3.7 trillion cells $\endgroup$ – Kappy Apr 20 '15 at 20:44
  • $\begingroup$ Even gene knockout in newborn animals is extremely difficult. Your only chance to get a complete knockout in all cells is probably at the single celled zygote stage. Knocking out, or down, expression in certain cells in an adult is possible, but gene delivery is still pretty difficult and results aren't guaranteed. $\endgroup$ – user137 Apr 20 '15 at 21:29
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Actually, Cas9 system might be a possible method to achieve your aim in the future, research teams are trying to utilize cas9 in vivo, which means maybe someday we can doing some genetic modification in body cell precisely. However, this is only a future direction and we still can not say its fit for a knockout.(Patrick D. Hsu, Eric S. Lander, and Feng Zhang, (2014) Development and Applications of CRISPR-Cas9 for Genome Engineering. Cell 14(6): 1262-1278) And for editing some cell gene in a limited area, some research are on going for therapeutic purpose (Liqun Zhang et al.CFTR Delivery to 25% of Surface Epithelial Cells Restores Normal Rates of Mucus Transport to Human Cystic Fibrosis Airway Epithelium), but haven't seen research are trying to built KO cell in vivo.

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  • $\begingroup$ thats all true, albeit speculative. Current Cas9/CRISPR efficiency is very low. around 10% for creating indels/knock-outs and around 0.1% for targeted genome integrations. In vitro you can get away with it because you don't inject/transfect single animal/cell. But in adult there should be some shotgun-like transfection with following selection. Which is very risky endeavor. $\endgroup$ – aaaaa says reinstate Monica Apr 21 '15 at 7:27
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    $\begingroup$ @aandreev Newer approaches increased the efficiency quite substantially, look at this post. It's again in vitro and I hardly see how that can be translated in vivo as such but I am confident this will greatly improve in the future. Also off targeting is still an issue for using CRISPR as a clinical treatment. A lot of work is being done in finding the best ways to predict the best sgRNAs for both efficiency and specificity. In essence I agree but I have good hopes. $\endgroup$ – cagliari2005 Apr 21 '15 at 7:48
  • $\begingroup$ i do have good hopes. However, paper you cite (NHEJ inhibition etc) seems to me like a novel way to screen: instead on neomycin authors rely on fact that cells with non-repairable NHEJ will most likely die. Hence increase in efficiency. $\endgroup$ – aaaaa says reinstate Monica Apr 21 '15 at 7:53
  • $\begingroup$ @aandreev. Nope, NHEJ and HR are two competing DNA repair mechanisms and it's not due to cell dying but rather HR being favored hence increased efficiency. $\endgroup$ – cagliari2005 Apr 21 '15 at 8:03
  • $\begingroup$ @cagliari2005 isn't it trinity: cell death/severe mutations, HR, NHEJ? sorry for off-topic, just to wrap up $\endgroup$ – aaaaa says reinstate Monica Apr 21 '15 at 8:24

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