You are viewing a single comment's thread from:
RE: Gene Drive and the Engineering of Extinction – Part I
Interesting. During the process of damaging the other allel, are there any negative side effects for the 'selfish gene'? Does it sometimes lead to self damage or termination of the whole cell? Or does it always execute and give it a 100% chance transmission when it is attempted?
Hi @kilbride, that's a very good question. I did not find any study on the question, but my guess is that these elements are generally integrated in non-coding regions of the genome or in gene introns, which reduces the risks of potential gene disruption during the transfer. I think that any homing endonuclease that would target an essential gene would have been eliminated during evolution.
The transmission efficiency is definitely not 100%, since homologous recombination is active only during certain phases of the cell cycle and not in every cell type, I think there is a significant proportion of cutting events that simply lead to the mutation of the recognition site of the enzyme, preventing recutting and the "copying" of the gene. The last figure is a bit misleading because too simplified, thank you for raising this question :)
Hi @kilbride and @carlgbush. I perform CRISPR/Cas9 gene editing in human pluripotent stem cells, so I am familiar with these topics. Yes, self damage and apoptosis (termination of the whole cell, "programmed cell death") can occur. Pretty much nothing in biology is 100%, so the desired editing events, particularly transmission of the gene of interest, is a fairly rare event. But, there are many things to consider when designing your gene targeting strategy. My understanding is that gene drive in its current form is more used to remove a gene from a population. Removing a gene is a much easier process than making a specific change because you are only relying on the repair machinery of the cell to accidentally repair the double stranded DNA break with an insertion or deletion (termed indel) of one or a few additional/less DNA bases, thus causing a frameshift mutation and essentially removing a gene product.
I would think to actually integrate the "homing endonuclease" (really a Cas9 and a few guide RNAs targeting the region of the genome that you want) directly into the gene that you want to remove would be most efficient, particularly if you were to add a stop codon just downstream of your homing endonuclease. So if the repair process is through homologous recombination, you will end up removing the gene that you wanted to target. However, if the repair process is non homologous end joining (NHEJ), you'll still remove the targeted gene of interest because you'll hopefully have created an indel, rendering the gene product functionally useless.
Hi @fighton, thank you for taking time to comment, you are completely right about gene drive. In this article I only talk about the natural occurrences and mechanisms of homing endonuclease, that's what @kilbride question was about. I will talk about Cas9 and how this mechanism is used for gene drive in the next article :)