CRISPR-Cas9-induced genetic mosaicism in three species of the microcrustacean Daphnia

Genetic mosaicism can arise from in vivo CRISPR-Cas9 gene editing, especially in the embryos. This study evaluates the extent of genetic mosaicism resulted from CRISPR-Cas9-mediated knockout for 11 genes in the freshwater microcrustacean Daphnia magna, D. pulex , and D. sinensis . Based on extensive genotyping data of the asexually produced progenies of successfully edited females, we find strong evidence of mosaicism in 9 of these genes. The genotyping data also suggest the gene editing activity can take place as early as the one-cell embryo stage and extends into the 32-cell and later stages. This study establishes genetic mosaicism as an important feature of Cas9-mediated gene editing in Daphnia .