Detection of CRISPR-Cas-induced mutations in Daphnia

Abstract

CRISPR-Cas9 has established itself as a robust tool for conducting loss of function gene research in emerging model species including the freshwater zooplankton Daphnia. However, sensitive detection of mutations, especially in genetic mosaic and pooled samples, remains a challenge. In this study we evaluate two of the most widely used mutation screening techniques, the T7 Endonuclease I (T7EI) assay and Fragment Analysis (FA) for their sensitivity, accuracy, and practical use in detecting CRISPR-induced indels in four targeted genes, DNMT3A, DNMT3B, PERIOD2, and DMRT1 in Daphnia magna. Here, we show that T7EI, although it offers a quick and cost-effective screening method, often produces false positives, especially when examining pooled samples. Conversely, FA facilitates detecting allele size differences at a fine resolution, reproducibility in detecting indels, and distinguishing zygosity and is more reliable as a method to detect mutation. Our comparative analyses convey the importance of carefully selecting the appropriate screening methods depending on research questions.

Keywords: Daphnia; T7 endonuclease; fragment analysis; mutants; screening.