Wanted to try a twitter tutorial (our first, so bear with it) on the v. interesting #CRISPR issues raised by the recent birth of #geneedited #Calf "Cosmo", thx to @UCDavis researcher @BioBeef. Author @MeganMolteni gamely brought in some perspective but no technical critic, so....
The following are issues neglected or barely raised in the text but should be born in mind while reading the article, which described attempts to add the SRY sex "determining" gene and make all male animals: wired.com/story/a-crispr…
2 The researchers began w/a "crude portrait" #genome sequence (so the first embryos died because the researchers chose the wrong place to edit). The premise of #geneediting is precision but this requires EXACT knowledge of the target genome, which almost invariably is lacking.
3 It starts to go even more wrong when, "To make the process easier", @BioBeef and co decided to also add a Green Fluorescent Protein gene, which will complicate their genetic and phenotypic analysis when it ends up being inserted into the genome.......
4 They then switch their #genome target from a sex chromosome to chromosome 17. "Since it was their final shot". It's a reason I suppose, but this leads to more trouble...
5 At one of the two newly chosen editing sites on Chromosome 17 "The cell randomly grabbed 26 DNA letters to fill the gap. (That’s pretty normal for how cells repair double-stranded DNA breaks.)"
Normal?!? From its beginning we have been assured that #geneediting is precise.
Normal?!? From its beginning we have been assured that #geneediting is precise.
6 At the other site (since there are 2 copies of every gene)
They found a bacterial plasmid in the genome at the edited site. (I hope they look for plasmids elsewhere in the genome too). But for heaven's sake why introduce a bacterial plasmid into cells you want to edit?
They found a bacterial plasmid in the genome at the edited site. (I hope they look for plasmids elsewhere in the genome too). But for heaven's sake why introduce a bacterial plasmid into cells you want to edit?
7 Ultimately, they found seven copies of the intended SRY gene and seven of GFP. That makes their "edited" cow part bacterium (multiple species no doubt) and part jellyfish. No info provided on any chromosomal DNA sequences lost. Bet big $$$ some will be.
8 In SRY and GFP copy numbers differed significantly with cell type. There are two likely explanations. The animal may be a chimera (in which some cells got edited at a different time point than others). Or the insert is unstable.
9 Re the complex DNA insertions, it should be pointed out that we wrote a review in 2007 on how damaging DNA to make transgenic organisms typically results in major DNA damage and v. complex insertions. Is @BioBeef too busy being innovative to read the literature? (ref 1 below)
10 “It’s an absolute nightmare to do knock-ins using Crispr,” More than interesting that researchers would say this and cite evidence but not publish this downside of #geneediting. How is scientific regulation supposed to work if negative results and downsides go unpublished?
11 But according to @UrnovFyodor, interviewed by @MeganMoltini, (and the researchers too) these errors are OK because these are "pioneering experiments". But notice the double standard:
12 On the one hand the researchers initially intended to breed from and commercialise this animal. They also tried to introduce their previous edited cows into the food supply (ref 2); but when the expt. goes wrong the work is described as cutting edge and so unpredictable.
13 Finally, they wanted to make a female (XX) genome male. But Cosmo is XY, i.e. naturally a male. He therefore provides no evidence that the "edits" introduced actually achieve the desired outcome. Oops. Unless Cosmo reproduces that $500,00 is largely wasted. @antonioregalado
