The key difference between transcriptional and posttranscriptional gene silencing is that transcriptional gene silencing is the regulation of gene expression at the transcriptional level in order to decrease RNA synthesis by promoter silencing while posttranscriptional gene silencing is the regulation of gene expression at translation level by sequence-specific RNA degradation.
Gene silencing is the process of regulating gene expression by interrupting or suppressing gene expression. It switches off certain types of genes. Therefore, it prevents the production of a protein from its corresponding gene. Gene silencing can happen during transcription or translation. Hence, there are two types of gene silencing as transcriptional gene silencing and posttranscriptional gene silencing. Transcriptional gene silencing decreases RNA synthesis while posttranscriptional gene silencing degrades mRNA. Moreover, transcriptional gene silencing takes place in the nuclei while posttranscriptional gene silencing takes place in the cytoplasm.
CONTENTS
1. Overview and Key Difference
2. What is Transcriptional Gene Silencing
3. What is Posttranscriptional Gene Silencing
4. Similarities Between Transcriptional and Posttranscriptional Gene Silencing
5. Side by Side Comparison – Transcriptional vs Posttranscriptional Gene Silencing in Tabular Form
6. Summary
What is Transcriptional Gene Silencing?
Transcriptional gene silencing is gene silencing which works through decreased RNA synthesis. It is a result of histone modification, creating an environment which is inaccessible to transcriptional machinery. This happens in the nuclei of cells. DNA methylation is very important for transcriptional gene silencing because the methylation of promoter sequence happens during the transcriptional gene silencing. Methylation of coding sequence does not affect the transcription. But, the methylation of promoter sequences results in promoter inactivation due to histone deacetylation and chromatin condensation. Once the promoters are silenced, it affects gene transcription. Hence, in transcriptional gene silencing, the promoters are silenced in order to regulate gene expression at the transcriptional level.
Figure 01: Gene Silencing
What is Posttranscriptional Gene Silencing?
Posttranscriptional gene silencing, also known as RNA silencing or RNA interference, is a type of gene silencing that works through sequence-specific degradation of RNA. Though the transcription of the gene is not affected, the protein synthesis from mRNA stops due to unstable or inaccessible mRNA. Posttranscriptional gene silencing is induced by the deliberate production of double-stranded RNA. Double-stranded RNA triggers the cleavage of homologous mRNA. Small interfering RNAs that have homologous sequences to transcribed regions of genes guide the sequence-specific degradation of mRNA. RNAi binds to the complementary portion of the target mRNA and tags it for degradation.
Figure 02: Posttranscriptional Gene Silencing
Posttranscriptional gene silencing has several applications, including gene therapy and cancer treatment. Posttranscriptional gene silencing is one of the natural defence mechanisms in plants against invading RNA viruses. Therefore, plants that are posttranscriptional gene silencing defective are more susceptible to infections by RNA viruses.
What are the Similarities Between Transcriptional and Posttranscriptional Gene Silencing?
- They are two distinct gene-silencing phenomena.
- Both phenomena can be induced by dsRNA.
- For both types of silencing, small RNA species are found, which are thought to be dsRNA decay products.
- They are mechanistically related.
What is the Difference Between Transcriptional and Posttranscriptional Gene Silencing?
Transcriptional gene silencing is a gene silencing phenomenon which operates at the transcription level via decreased RNA synthesis. On the other hand, posttranscriptional gene silencing is a gene silencing phenomenon which occurs at translation level via sequence-specific degradation of mRNA. Thus, this is the key difference between transcriptional and posttranscriptional gene silencing.
Moreover, transcriptional gene silencing occurs in the nuclei while posttranscriptional gene silencing occurs in the cytoplasm. Besides, promoters are inactivated in transcriptional gene silencing while promoters are active in posttranscriptional gene silencing.
Below infographic tabulates more differences between transcriptional and posttranscriptional gene silencing.
Summary – Transcriptional vs Posttranscriptional Gene Silencing
Genes are regulated at either the transcriptional or posttranscriptional level. Transcriptional gene silencing occurs in the nuclei via promoter sequence methylation and histone modification. As a result, RNA synthesis decreases. Posttranscriptional gene silencing occurs in the cytoplasm through the cleavage of mRNA and inhibition of translation. Both phenomena are induced by dsRNA and depend on small interfering RNAs. Thus, this summarizes the difference between transcriptional and posttranscriptional gene silencing.
Reference:
1. Hoffer, Paul, et al. “Posttranscriptional Gene Silencing in Nuclei.” PNAS, National Academy of Sciences, 4 Jan. 2011, Available here.
Image Courtesy:
1. “RNAi-simplified” – adapted from one by Matzke MA, Matzke AJM – This figure is adapted from one by Matzke MA, Matzke AJM (2004) Planting the Seeds of a New Paradigm. PLoS Biol 2(5): e133 doi:10.1371/journal.pbio.0020133. (CC BY 2.5) via Commons Wikimedia
2. “Part 1 of basic mechanism of post-transcriptional gene silencing in mammals” By Mertmetin96 – Own work (CC BY-SA 4.0) via Commons Wikimedia