Conditional mutagenesis strategies in zebrafish

Targeted nucleases have enabled engineering of conditional zebrafish mutants for reverse genetics. Conditional mutagenesis relies on tissue- and/or cell type-specific expression of the tamoxifen-inducible Cre recombinase. Floxed alleles, gene traps, and inducible expression of CRISPR (clustered regularly interspaced short palindromic repeats)-associated protein 9 (Cas9) have all been successfully used for conditional mutagenesis in zebrafish. Mutagenicity cassettes have been successfully integrated into target loci by both homology-directed repair and nonhomologous end joining. Gene disruption or knockout is an essential tool for elucidating gene function. Conditional knockout methodology was developed to further advance these studies by enabling gene disruption at a predefined time and/or in discrete cells. While the conditional knockout method is widely used in the mouse, technical limitations have stifled direct adoption of this methodology in other animal models including the zebrafish. Recent advances in genome editing have enabled engineering of distinct classes of conditional mutants in zebrafish. To further accelerate the development and application of conditional mutants, we will review diverse methods of conditional knockout engineering and discuss the advantages of different conditional alleles. Gene disruption or knockout is an essential tool for elucidating gene function. Conditional knockout methodology was developed to further advance these studies by enabling gene disruption at a predefined time and/or in discrete cells. While the conditional knockout method is widely used in the mouse, technical limitations have stifled direct adoption of this methodology in other animal models including the zebrafish. Recent advances in genome editing have enabled engineering of distinct classes of conditional mutants in zebrafish. To further accelerate the development and application of conditional mutants, we will review diverse methods of conditional knockout engineering and discuss the advantages of different conditional alleles.