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.