Making gynogenetic diploid zebrafish by early pressure

Area of Science:

• Genetics
• Developmental Biology
• Molecular Biology

Background:

• Genetic studies in diploid eukaryotes are often complicated by heterozygosity.
• Accelerated forward genetic screens require methods to produce homozygous diploid offspring from heterozygous females.

Purpose of the Study:

• To describe and validate the early pressure (EP) method for generating homozygous diploid zebrafish.
• To enable direct screening of mutagenized F1 females for deleterious mutations.

Main Methods:

• Zebrafish eggs are activated with UV-inactivated sperm.
• Physical treatments (heat or pressure) are used to block either meiosis II or the first zygotic cell division, preventing microtubule polymerization.
• The "early pressure" (EP) method specifically blocks meiosis II shortly after fertilization.

Main Results:

• The EP method yields a high percentage of viable embryos that develop into fertile adults.
• Embryos are homozygous at all loci, except those separated from their centromere by meiosis I recombination.
• Homozygous mutations are detected with high efficiency for centromeric loci (up to 50%) and lower efficiency for telomeric loci (less than 1%).

Conclusions:

• The early pressure (EP) method is a robust technique for generating homozygous diploid zebrafish.
• This method significantly accelerates forward genetic screens by allowing direct screening of mutagenized F1 females.
• The EP method facilitates the identification of homozygous mutations across the zebrafish genome.