Question 1

How does RNA interference work to silence genes in C. elegans?

Accepted Answer

Double-stranded RNA enters C. elegans cells after ingestion. The enzyme Dicer cleaves dsRNA into short interfering RNA (siRNA), 21-23 nucleotides long. The siRNA associates with the RNA-induced silencing complex (RISC) and binds target mRNA via complementary base pairing, leading to mRNA degradation and gene knockdown.

Question 2

What is the first step in preparing bacteria for RNAi experiments?

Accepted Answer

Transform the plasmid encoding your target dsRNA into HT115(DE3) E. coli strain, which lacks RNA polymerase III and contains an IPTG-inducible T7 DNA polymerase gene. Also transform bacteria with an empty plasmid as a control. Spread transformed bacteria on LB agar plates containing tetracycline and carbenicillin, then incubate overnight at 37°C.

Question 3

Why is worm synchronization important before RNAi treatment?

Accepted Answer

Synchronizing developmental stages ensures that observed phenotypic differences result from gene knockdown rather than developmental variation. Transfer L4 worms to RNAi plates overnight at 20°C to become young adults, then move them to new plates for 6-8 hours to lay eggs. This produces developmentally synchronized progeny for analysis.

Question 4

How do researchers use RNAi to perform reverse genetic screens?

Accepted Answer

Reverse genetic screens knock down known genes from a library and assess phenotypic results to discover gene function. Researchers culture bacteria expressing dsRNA for many C. elegans genes on multi-well plates and feed them to worms. Phenotypic effects reveal normal in vivo gene functions and can be automated for high-throughput analysis of thousands of genes.

Question 5

What happens during the bacterial culture preparation phase?

Accepted Answer

Select a single bacterial colony and add it to 1 ml LB broth with 100 μg/ml ampicillin. Incubate overnight at 37°C with agitation. Then add 5 ml fresh LB broth with ampicillin and incubate 4-6 hours at 37°C. This culture is then added to RNAi worm plates and incubated overnight at 37°C to create a bacterial lawn.

Question 6

What phenotypes can be observed when analyzing RNAi-treated worms?

Accepted Answer

Compare RNAi knockdown worms with controls and note differences in size, developmental stage, morphology, and localization patterns of fluorescently tagged proteins. Scientists can also assess developmental timing effects, such as genes that delay development when knocked down, or genes involved in organ development and other biological processes.

Question 7

How is a microscope slide prepared to visualize C. elegans?

Accepted Answer

Tape two glass slides with labeling tape as spacers. Place a clean slide between them and pipet 150 μl of 4% molten agar onto it. Cover with a perpendicular slide, then gently separate. Add 10 μl sodium azide anesthetic to the agar pad, transfer worms using a platinum wire pick, add a cover slip, and observe under a microscope.

RNAi in C. elegans - חידון הערכה