The overall goal of this breeding strategy is to manipulate mutant penetrance upward or downward. This selective breeding method enables a more complete understanding of mutant phenotypes. By generating high and low penetrance mutant strains, the entire phenotypic series of a mutation can be understood.
Most zebrafish scale where mutants are recessive lethal, so homozygous mutants die before they can be directly bred. Therefore, we employ the classical selective breeding strategy of progeny testing, which we demonstrate here. We first had the item for this method when attempting to time lapse record ectopic bone cell development.
Frustratingly, extra bone cells appeared in it frequently, so we set out to alter mutant penetrants by selective breeding. Although we perform this method on a zebrafish scale with a mutant line, it can also be applied to other zebrafish mutant phenotypes and likely, other organisms. After preparing unselected starting zebrafish stock according to the text protocol, carry out KASP genotyping as follows.
Place the zebrafish tail tissue in 50 microliters of lysis buffer in the wells of a 96 well plate. Add 10 microliters of 10 milligrams per milliliter proteinase k per well and digest the tissue samples in a thermocycler at 55 degree celsius for two to five hours. Followed by a 20 minute 94 degree celsius inactivation step.
Refrigerate the lysis product after digestion. Use a spectrophotometer to quantify the genomic DNA. Then, using molecular biology grade water, dilute the genomic template so that each reaction contains approximately 20 to 30 nanograms.
Add 0.14 microliters of the KASP primer mix and five microliters of the KASP master mix per sample on ice, into a 1.5 milliliter microcentrifuge tube and mix well. Then, briefly centrifuge to collect the contents at the bottom of the tube. Pipette five microliters of primer master mix solution into the wells of a 96 well optical PCR plate suitable for the real time PCR machine being used.
Then, pipette five microliters of diluted DNA template samples into each well and aspirate with a pipette to mix. Place an optically clear film seal over the plate, ensuring that the film is fully sealed on each well. Briefly centrifuge the plate at 600 x G to collect the contents at the bottom and to remove bubbles from the mix.
After performing the main KASP reaction, view the resulting scatter plot produced by the analysis computer. House the identified heterozygous animals together on the main water system. After the animal recover from the fin clip, set up pairwise intercrosses, use dividers to ensure embryos are synchronized.
Collect the embryos, and keep the parental pairs isolated in breeding cages. Monitor isolated adults, so that aggressive fish can be separated or provided with cover. To rear the embryos on day five or six, when the swim bladders is inflated in 75%of a clutch, use a glass pipette to collect phenotypically wild type animals.
Place phenotypic wild types in the nursery, recording which parents yielded them. After anesthetizing larvae that do not inflate their swim bladders according to the text protocol, use a wide bore glass pasteur pipette to collect the animals into 1.5 milliliters microcentrifuge tubes. Remove the embryo water from each tube and replace it with one milliliter of 2%paraformaldehyde in 1x PBS.
Rock the tubes for one hour to fix the animals. Track the tubes regularly during this and all subsequent rocking steps to ensure no larvae have become stuck to the side or clumped in the bottom of the tube. Use a glass pipette to remove the fixative from the tubes.
Then add one milliliter of 50%ethanol. Rock the samples for an additional 10 minutes. Prepare fresh staining solution by adding 20 microliters of 0.5%alizarin red per one milliliter of Alcian premix.
Remove the 50%ethanol, and add one milliliter of staining solution to each tube. Then, rock the tubes overnight. Within a few days after bleaching the embryos according to the text protocol, score stained mutant offspring for penetrants.
In this example, we score for any occurrence of a topic bone. For the next generation, choose two high penetrants and two low penetrants families. Give each parental pair a sub stock identifier, for example, family 4.01, 02, et cetera.
It's also helpful to indicate the or inbred generation number on all labels. House parental pairs on the main system with several mixed sex companion fish. Companion fish can be any zebrafish line with permanent obvious distinguishing features, such as altered pigmentation or fin structure.
Label the tanks containing the wild type sibling larvae from selected families with the penetrants from the mutant siblings and raise the fish to adulthood as normal. Selective breeding by progeny testing, should yield a shift in overall penetrants both downward and upward in a few generations. In these examples, apply to the mef2ca b1086 mutant, high or low penetrants of a topic bone between the opercal and the branchiostegal ray in lethal homozygous mutants was selected for.
In a successful cast procedure, type groupings of samples corresponding to gene type should be recognized by the computer program and the NTCs should be located near the origin of the plot after sufficient cycles have been performed. As demonstrated here, successful Alcian blue, alizarin red stain will have vibrantly stained bone and cartilage elements that are not transparent or faint. The boundaries of the cartilage elements should appear crisp and individual contracytes will be discernible.
Alcian blue that is too concentrated were not clear from other tissues making analysis impossible. Implementing this technique from zebrafish line maintenance will likely alter penetrants in a few generations. Following this procedure, other methods like NC2 hybridization and timelapse imaging studies may yield more consistent results.
We use this technique to explore the heritability of phenotype variation. After watching this video, you should have a good understanding of how to selectively breed your mutant strains to alter penetrance, even if the mutation is lethal.
