PCR-Based Genotyping of Zebrafish Genetic Mutants

Abstract

Zebrafish genetic mutants have emerged as a valuable model system for studying various aspects of disease and developmental biology. Mutant zebrafish embryos are generally identified based on phenotypic defects at later developmental stages, making it difficult to investigate underlying molecular mechanisms at earlier stages. This protocol presents a PCR-based genotyping method that enables the identification of wild-type, heterozygous, and homozygous zebrafish genetic mutants at any developmental stage, even when they are phenotypically indistinguishable. The approach involves the amplification of specific genomic regions using carefully designed primers, followed by gel electrophoresis. This genotyping method facilitates the investigation of the molecular mechanisms driving phenotypic defects that are observed at later timepoints. This protocol allows researchers to perform analyses such as immunofluorescence, RT-PCR, RNA sequencing, and other molecular experiments on early developmental stages of mutants. The availability of this protocol expands the utility of zebrafish genetic mutants for elucidating the molecular underpinnings of various biological processes throughout development. Key features • Enables genotyping of zebrafish genetic mutants at any developmental stage, even before the onset of phenotypic defects. • Utilizes PCR amplification and restriction enzyme digestion to distinguish wild-type, mutant, and heterozygous genotypes.

Keywords: Developmental biology; Embryos; Genotyping; Model organism; Mutant analysis; PCR; Phenotypic defects; Restriction enzyme digestion; Zebrafish.

Figure 1.. Male and female zebrafish separated by mating divider in a breeding tank

Figure 2.. Zebrafish embryos are observed below the breeding mesh

Figure 3.. Schematic representation of the recommended tail fin clipping site, indicated by the dashed line.

(A) Embryo. (B) Adult fish.

Figure 4.. Genotyping of 20 embryos produced by banp^rw337 heterozygous parent fishes.

When genomic DNA containing a banp^rw337 mutation site is amplified with PCR using a specific set of primers, subjected to MboII digestion, which cuts only the mutant-derived genomic DNA, and fractionated by electrophoresis in a 4% agarose gel, three band patterns appear: a single upper band at 239 bp for wild-type embryos (magenta), a single lower band at 212 bp for homozygous mutant embryos (green), and two bands at 212 and 239 bp for heterozygous embryos (white). The right-most lane indicates the DNA ladder maker.

Figure 5.. Toluidine blue–stained tissue morphology of banp^rw337 wild-type vs. homozygous mutants at 54 hours post fertilization (hpf).

(A) Wild-type embryo head. (B) Wild-type retina. (C) banp^rw337 mutant embryo head. (D) banp^rw337 mutant retina. C and D show pyknotic cells indicating cell death. The red arrow indicates pyknotic cells. Scale bars: 20 μm. Adapted from [5].