Maternal products are those mRNAs and proteins deposited during oogenesis, which play critical roles in controlling oocyte formation, fertilization, and early embryonic development. However, loss-of-function studies for these maternal factors are still lacking, mainly because of the prolonged period of transgenerational screening and technical barriers that prevent the generation of maternal (M) and maternal and zygotic (MZ) mutant embryos. By the transgenic expression of multiple sgRNAs targeting a single gene of interest in the background of a transgenic line Tg(zpc:zcas9) with oocyte-specific cas9 expression, we have successfully obtained maternal or maternal-zygotic mutant for single genes in F1 embryos. In this work, we tandemly connected a maternal GFP marker and eight sgRNA expression units to target dvl2 and dvl3a simultaneously and introduced this construct to the genome of Tg(zpc:zcas9) by meganuclease I-Sce I. As expected, we confirmed the existence of Mdvl2;Mdvl3a embryos with strong defective convergence and extension movement during gastrulation among outcrossed GFP positive F1 offspring. The MZdvl2;MZdvl3a embryos were also obtained by crossing the mutant carrying mosaic F0 female with dvl2+/-;dvl3a-/- male fish. This proof-of-principle thus highlights the potential of this conditional knockout strategy to circumvent the current difficulty in the study of genes with multiple functionally redundant paralogs.
Keywords: CRISPR/Cas9; conditional knockout; double mutant; early development; maternal factors; oocyte; zebrafish.