Biology
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Using Caenorhabditis elegans to Screen for Tissue-Specific Chaperone Interactions
Chapters
Summary June 7th, 2020
To study chaperone-chaperone and chaperone-substrate interactions, we perform synthetic interaction screens in Caenorhabditis elegans using RNA interference in combination with mild mutations or over-expression of chaperones and monitor tissue-specific protein dysfunction at the organismal level.
Transcript
The overall goal of the following experiment in genetically trackable design Caenorhabditis elegans is to identify tissue-specific chaperone interactions. The main advantage of this technique is that it combines easy to use assays such as fitting Golan AI and behavioral readouts to expose novel tissue specific interactions. For a non-stressful embryo synchronization, use a worm pick to move about 100 eggs from an unsynchronized worm plate to a newly seated NGM plate and cultivate the animals according to the appropriate experimental schedule.
When the animals reach the first day of egg-laying, slowly add one milliliter of M9 buffer to the plate, distant to the bacterial lawn, and rotate the plate so that the buffer completely covers the plate. Tilt the plate to one side to remove the liquid and wash the animals from the plate. When all of the worms have been washed from the plate, use a standard plastic pipette tip to cut a square of Agar around where the eggs are concentrated and place the piece of Agar onto a newly seated NGM plate.
Cultivate the eggs under the same culture conditions. At the end of the incubation, the plate should be covered with synchronized eggs. After washing all of the animals from the plate as just demonstrated, add one milliliter of fresh M9 buffer and use a cell scraper to release the eggs from the plate.
When all of the eggs have been detached, transfer the entire volume of buffer from the plate into a conical tube for centrifugation. Centrifuge the tube and discard the supernatant. After removing the supernatant, add up to one milliliter of fresh M9 buffer to the plate and pipette to resuspend the eggs.
Wash the eggs five more times as just demonstrated. After the last wash, the egg pellet should appear white and all but the last 200 microliters of supernatant can be removed. To cultivate synchronized nematodes for an experiment, place a drop of about 30 eggs close to the bacterial lawn and each interference RNA seated plate and about 30 eggs onto a plate seated with empty vector containing bacteria.
Then cultivate the animals under the appropriate culture conditions according to the experimental protocol. To assess the embryonic lethality of the synchronized animals, when the animals begin to lay eggs, transfer about 100 eggs to an empty plate and spread the eggs into rows to simplify the counting. After 24 to 48 hours, score the percent of unhatched eggs.
For reference, compare the experimental animal eggs to the eggs of animals treated with empty vector control bacteria. To set up a paralysis assay, cultivate age-synchronized animals on empty vector control bacteria, until the animals reach adulthood, but before egg-laying starts. Use a fine marker to draw a line on the back of a regular NGM Agar plate, and place five to ten animals on the marked line.
Set a timer for 10 minutes and score the percentage of animals remaining on the line as paralyzed worms. For reference, compare this data to the percentage of mutant animals grown on empty vector control bacteria. For Protein Knockdown Validation, place 250 to 300 synchronized eggs onto a 60 millimeter NGM interference RNA plate seated with the relevant double stranded RNA expressing or empty vector containing bacteria, and cultivate the eggs for the appropriate experimental period.
At the end of the incubation, transfer a total of 200 young adult animals into the cap of a 1.5 milliliter tube containing 200 microliters of PBST maintained at the animals cultivation temperature. Close the cap carefully, and centrifuge the animals at 1000 times G for 1 minute. At the end of the centrifugation, add 800 microliters of fresh PBST to the tube and centrifuge the worms again.
Carefully remove the top 900 microliters of the supernatant, and wash the nematodes in fresh PBST 3 more times as just demonstrated. After the last wash, remove all but the last 100 microliters of the supernatant and add 25 microliters of 5X sample buffer to the animals. Heat the samples for 10 minutes at 92 degrees Celsius and 1000 revolutions per minute, before loading 20 microliters of each sample onto an SDS page gel.
Then perform Western blot analysis using the appropriate antibodies to determine the relative stability of the protein of interest, and use densitometric software to determine the intensity of the bans. HSP6 knocked down during development results in a strong developmental arrest in wild type animals. At the same time, HSP6 knocked down in a muscle specific interference RNA strain expressing wild-type RDE1 in muscle tissue does not cause developmental arrest.
Whereas HSP6 knocked down an intestine specific RNAI strain expressing wild type RDE1 in intestinal cells, results in a strong developmental arrest and phenotype. A mutation in HSP6 MG585 that causes a mild growth delay, can, therefore, be used to screen for aggravating or alleviating chaperone interactions by crossing a strain carrying that mutated gene into an intestinal specific interference RNA strain, and screening the chaperone interference RNA library. Myosin organization and UNC45 mutant animals treated with STI1 AHSA1 or DAF41 interference RNA, is similar to that of wild type worms at the fourth larval stage.
Although the mutants exhibit disrupted sarcomeres after reaching adulthood. In contrast, both UNC45 mutant animals treated with an empty vector control and wild type animals remain unaffected. Genetic interactions are not indicative of physical interaction.
Thus, follow-up experiments using genetic interaction screen must be performed to validate and directly examine the nature of the identified interactions.
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