You are right (at the 8 cell stage you can still separate them and treat them one at a time, giving you multiple shots at IVF)
Two of the main issues regarding gene editing when not talking single cells are the transfer into the nucleus, and then accessing the DNA you want.
In bacteria, the DNA kinda just swims around in the cell, which makes editing easy if you can get the CRISPR/Cas9 complex in the cell. But animal cells have another membrane surrounding the DNA, making the transfer less than straightforward.
Regarding access: our DNA isn’t lying around like mom’s spaghetti, but rather pretty tightly packed around histones - a protein octamer.
This means that your target might not be reachable (the cell itself has 3 options iirc: slide the DNA over the surface of the histone, replace a part of the histone with an alternative, or remove the histone altogether) Since the way the DNA is wound around the histones affects gene activity (something tightly packed is not active, something in a loose area is getting transcribed into mRNA and therefore possibly active), you cannot just unwind all of it.
The only time this is not the case is during cell division, where the nucleus is getting dismantled so the DNA can be duplicated and both new cells can get their own copy. But many cells do not divide in an adult (except for a reservoir of stem cells which are there to replace lost cells)
from what i remember (it’s been a few years since i studied this stuff lol) you can only arrest the cell cycle (dismantling -> duplication of chromosomes -> separation of chromosomes -> completion of division) at specific points, and can’t go in reverse. Theres a whole cascade of signals, that when started, are running their way to specific checkpoints. if a cell is stuck for too long at any checkpoint, it commits suicide, because that’s THE sign for unrecoverable DNA damage. And if a cell starts ignoring checkpoints and suicide signals, it’s called cancer.
Many antibiotics work that way btw - they look a lot like nucleotides (A C G T), but if a bacterium adds them when copying instead of one of the “letters”, the machinery gets stuck, and the bacterium cant divide anymore. That gives the immune system time to kill them off. Bacteria replicate a lot and have no proofreading of what they are copying, so they are susceptible to this. Animal cells have proofreading AND the ability to correct an error, so we are fine.
I loved studying this stuff. i did NOT love the crapload of chemistry i had to learn, but even that was highly interesting.
You are right (at the 8 cell stage you can still separate them and treat them one at a time, giving you multiple shots at IVF)
Two of the main issues regarding gene editing when not talking single cells are the transfer into the nucleus, and then accessing the DNA you want.
In bacteria, the DNA kinda just swims around in the cell, which makes editing easy if you can get the CRISPR/Cas9 complex in the cell. But animal cells have another membrane surrounding the DNA, making the transfer less than straightforward.
Regarding access: our DNA isn’t lying around like mom’s spaghetti, but rather pretty tightly packed around histones - a protein octamer.
This means that your target might not be reachable (the cell itself has 3 options iirc: slide the DNA over the surface of the histone, replace a part of the histone with an alternative, or remove the histone altogether) Since the way the DNA is wound around the histones affects gene activity (something tightly packed is not active, something in a loose area is getting transcribed into mRNA and therefore possibly active), you cannot just unwind all of it.
The only time this is not the case is during cell division, where the nucleus is getting dismantled so the DNA can be duplicated and both new cells can get their own copy. But many cells do not divide in an adult (except for a reservoir of stem cells which are there to replace lost cells)
So, it’s all very complicated.
deleted by creator
from what i remember (it’s been a few years since i studied this stuff lol) you can only arrest the cell cycle (dismantling -> duplication of chromosomes -> separation of chromosomes -> completion of division) at specific points, and can’t go in reverse. Theres a whole cascade of signals, that when started, are running their way to specific checkpoints. if a cell is stuck for too long at any checkpoint, it commits suicide, because that’s THE sign for unrecoverable DNA damage. And if a cell starts ignoring checkpoints and suicide signals, it’s called cancer.
Many antibiotics work that way btw - they look a lot like nucleotides (A C G T), but if a bacterium adds them when copying instead of one of the “letters”, the machinery gets stuck, and the bacterium cant divide anymore. That gives the immune system time to kill them off. Bacteria replicate a lot and have no proofreading of what they are copying, so they are susceptible to this. Animal cells have proofreading AND the ability to correct an error, so we are fine.
I loved studying this stuff. i did NOT love the crapload of chemistry i had to learn, but even that was highly interesting.
I personally loved my microbiology’s professor summary of this: “For microbes, if you’re not growing, you’re going.”