Generation of eGFP and Cre knockin rats by CRISPR/Cas9. FEBS Journal. Accepted manuscript online: 17 JUL 2014.
A key ratio to scrutinize is the ratio of targeted insertions to the total number of insertions and other mutations, e.g. indels. The reason is that the total number reflects the number of pups in which CRISPR clearly had activity. Therefore the ratio reflects the proportion of the time that the HDR process occurred successfully as a subset of all embryos that had some sort of CRISPR-mediated cleavage event. Since almost all of their live pups had evidence of the HDR insertions or indels anyway, the ratio of targeted/all events is still about 25-50%.
How big were the homology arms used? Between ~1.5 to 2.1 kb in all cases (3 constructs x 2 arms each = 6 arms total). Concentrations used were: 25 ng/µl Cas9 mRNA, 10 ng/µl, and 4 ng/µl of the donor plasmid in circular form.