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Starting from Scratch with RNA Interference: What You Need to Know

Release time：2026-04-09 16:17:54

Gene silencing is an important method for regulating gene expression in eukaryotic cells. RNA interference (RNAi) is an effective tool for this, inhibiting gene expression by blocking the transcription or translation of specific genes.

Key Points of RNAi Technology Applications:

It is crucial to use the appropriate method to deliver exogenous small interfering RNA (siRNA) into the target organism. After a series of biochemical pathways, this triggers the RNA interference effect.

Sources of siRNA

1. In vitro synthesis
siRNA fragments are synthetically made, amplified by PCR, and then introduced into target cells. Disadvantages: The effectiveness depends on the transfection efficiency of the cells, and it does not allow for long-term RNA interference.

Table 1: Comparison of Various In Vitro siRNA Synthesis Methods

Name	Synthesis Method	Applicable	Not Applicable
Chemical Synthesis	Direct synthesis	When the most effective siRNA has already been found; need large quantities of siRNA	Screening of siRNAs need long-term research
In vitro Transcription	Transcription using DNA oligos as templates	Screening of siRNAs; when the cost of chemical synthesis becomes a barrier	Need large quantities of a specific siRNA and long-term research
RNase III Digestion	RNase III digestion of long double-stranded RNA fragments	Quick and cost-effective study of gene function loss phenotypes	Long-term research projects; specific siRNAs (e.g., gene therapy)

2.In vivo synthesis
The required siRNA fragments are introduced into the target cells using a vector. This method overcomes the limitations of artificially synthesizing siRNA in vitro.

Designing siRNA Vectors

Plasmids are typically used as vectors to deliver siRNA into cells. The introduced vector can produce hairpin-shaped siRNA (shRNA) in vivo, similar to miRNA.
The designed vector DNA should include the following components:
1. Sense strand: This sequence is the same as the gene sequence required for transcribing the target mRNA in the organism.
2. Antisense strand: This strand is complementary to the sense strand, and its transcription yields siRNA that is complementary to the target mRNA.
3. Non-complementary sequence: This ensures that the vector forms a hairpin structure after transcription.
4. Restriction enzyme sites: Such as BamH I & Hind III for cleavage.

Designing siRNA Sequences

In addition to selecting the appropriate siRNA vector, the following points must be considered when designing siRNA sequences:

1. Design the ends to contain 5-6 A (T)

siRNA vectors are transcribed by RNA polymerase III, which can transcribe most small RNA segments in mammals. A characteristic of RNA polymerase III is that transcription stops when it reaches 5-6 adenine nucleotides (A), so the transcribed siRNA vector will have 5-6 uracil (U) at the 3' end.

2. Select 2-5 different parts of the target gene sequence
Target mRNA in the organism may have certain regions bound by regulatory proteins, making RNAi less effective. Thus, it is necessary to select different gene fragments for transcription to improve the efficiency of gene expression suppression.

Principles for Selecting RNAi Target Sequences

1. Start from the AUG initiation codon of the transcript (mRNA) and look for the "AA" dinucleotide sequence. Record the 19 base sequence at its 3' end as a potential siRNA target site. Studies have shown that siRNAs with a GC content of 45%-55% are more effective than those with higher GC content.

2. Compare the potential sequences with the corresponding genome database (e.g., human, mouse, rat) to exclude sequences that are homologous to other coding sequences/ESTs. For example, use BLAST for experimental comparison (https://blast.ncbi.nlm.nih.gov/Blast.cgi).

3. Select appropriate target sequences for synthesis. Typically, multiple target siRNA sequences are designed for a gene to identify the most effective siRNA.

Negative Control

A complete siRNA experiment should include a negative control. The siRNA used as a negative control should have the same composition as the selected siRNA sequence, but should not show significant homology with the target mRNA. Typically, the selected siRNA sequence is scrambled, and results should be checked to ensure that it has no homology with other genes in the target cells.

RNA Interference Efficiency Detection

Efficiency should generally be assessed at three levels: mRNA, protein, and cellular phenotype.
🔹mRNA level: Can be detected using RT-PCR or Real-time PCR.
🔹Protein level: Detection can be done via Western blot, ELISA, or immunohistochemistry.
🔹Cellular phenotype level: Can be evaluated using methods such as MTT, colony formation assays, flow cytometry, or cell chamber experiments.

Example Case

Lewandowski et al. used AAV-mediated expression of shRNA to suppress PTEN expression in adult rats, leading to increased phosphorylation of ribosomal protein pS6.

Figure 1: AAV-mediated suppression of PTEN expression in the cortex of adult rats via intraparenchymal injection. (Lewandowski, et al., Journal of Neuroscience, 2014)

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Starting from Scratch with RNA Interference: What You Need to Know

Key Points of RNAi Technology Applications:

Sources of siRNA

Designing siRNA Vectors

Designing siRNA Sequences

Principles for Selecting RNAi Target Sequences

RNA Interference Efficiency Detection

Example Case

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Starting from Scratch with RNA Interference: What You Need to Know

Key Points of RNAi Technology Applications:

Sources of siRNA

Designing siRNA Vectors

Designing siRNA Sequences

Principles for Selecting RNAi Target Sequences

RNA Interference Efficiency Detection

Example Case

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