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[deleted] t1_iy1p3dl wrote

The only reason i could think for this being true would be that DNA is more accessible during cell division as opposed to being in a typically condensed state that would be inaccessible to Cas9 binding. It seems like something that would be pretty context dependent and depend on the gene.

Do you have a reference for what phenomenon you are talking about?

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Waizac123 t1_iy2rkpv wrote

The nuclear envelope is also broken down during mitosis - which would help if CRISPR is unable to normally enter the nucleus.

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phriendlyphellow t1_iy2hqay wrote

There are two ways the cell can fix the double stranded break (DSB): Non-homologous End Joining (NHEJ), which is sloppy, and Homology Directed DNA Repair (HDR), which is cleaner but limited to two stages of the cell cycle.

This article describes the challenge.

“Given that HDR is restricted to the S and G2 phases of the cell cycle, only present in dividing cells, this approach might not be suitable for editing and repairing the genome in non-dividing cells.”

Here is the original paper that the above website sites as a source.

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deisle t1_iy25psm wrote

I mean if you're coming from the view of "does this change now have an effect on the whole organism" the answer would be yeah kinda. If you wanted to delete a gene and see what effect it had, if you only cha get one cell's genome, you'll never see an effect because it's just one cell out of millions/billions/trillions. On the other hand, if you inject the CRISPR stuff in a fertilized egg at the si gle cell stage, that cell will divide a bunch and then all the cells will have the deletion. Those are the two extremes, so you can target stem cells or remove blood cells and return them, but the idea is the same: you need to change enough of the correct cells to see an effect

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CrateDane t1_iy51kwm wrote

CRISPR-Cas9 can cut the DNA in cells whether or not they are dividing.

The problem arises if you then try to rely on HDR to insert a sequence at the break. The HDR pathway is inactive in non-dividing cells, so that strategy will not work. But there are other ways to insert DNA in this scenario, for example HITI. And if you are not trying to insert DNA, but just knock out a gene, it will work anyway.

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SheScientist t1_iy6dmwb wrote

Yes! You can also be hindered by HDR when you want to knock out a gene in dividing cells. This was an unfortunate end to one of my grad school experiments. I knocked out a gene in a system where cells were rapidly dividing, and instead of getting a nice knockout, I got less than 10% editing in vivo because HDR is preferred during cell division when the sister chromatid is nearby. I get better knockout in that system when cells are dividing infrequently.

The answer to the OP’s question is definitely that CRISPR works no matter if cells are dividing, but how well and how permanently it works depends on the system, the type of edit, and a whole host of other factors.

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