Microrna biogenesis pathway

Definition

The microrna biogenesis pathway is a cellular process that generates microRNAs (miRNAs) from primary transcripts, leading to the regulation of gene expression at the post-transcriptional level. This pathway involves several key steps including transcription, processing by specific enzymes, and incorporation into the RNA-induced silencing complex (RISC), which ultimately leads to target mRNA degradation or repression.

5 Must Know Facts For Your Next Test

1. The microrna biogenesis pathway begins with the transcription of primary miRNA (pri-miRNA) by RNA polymerase II.
2. After initial transcription, the Drosha enzyme cleaves pri-miRNA into shorter precursor miRNA (pre-miRNA) segments in the nucleus.
3. Dicer processes pre-miRNA into mature miRNA in the cytoplasm, which typically consists of 20-24 nucleotides.
4. Mature miRNAs are then loaded onto RISC, where they guide the complex to target mRNAs based on sequence complementarity.
5. The binding of miRNAs to target mRNAs usually results in translational repression or degradation of the target mRNA, thus regulating gene expression.

Review Questions

• Explain how Drosha and Dicer contribute to the microrna biogenesis pathway and their roles in miRNA processing.
  • Drosha and Dicer are two crucial enzymes in the microrna biogenesis pathway. Drosha initiates the process by cleaving primary miRNA transcripts into precursor miRNAs within the nucleus. Following this, Dicer further processes these precursor miRNAs in the cytoplasm into mature miRNAs. Both enzymes ensure that miRNAs are correctly processed and functional for their role in gene regulation.
• Discuss the significance of RISC in the function of mature miRNAs and how it affects target mRNA expression.
  • The RNA-induced silencing complex (RISC) is essential for the action of mature microRNAs. Once loaded with a mature miRNA, RISC binds to target mRNAs that have complementary sequences. This interaction typically results in either translational repression or degradation of the target mRNA, effectively modulating gene expression post-transcriptionally. The ability of RISC to silence genes makes it a vital player in cellular regulation and development.
• Evaluate the implications of disruptions in the microrna biogenesis pathway on gene regulation and potential disease outcomes.
  • Disruptions in the microrna biogenesis pathway can lead to abnormal levels of miRNAs, which can significantly impact gene regulation. Such dysregulation has been linked to various diseases, including cancer, where overexpression or underexpression of specific miRNAs can promote tumorigenesis or suppress tumor suppressor genes. Understanding these implications helps researchers identify potential therapeutic targets for diseases linked to miRNA dysfunction, illustrating the importance of maintaining a well-functioning biogenesis pathway.

Related terms

Drosha: A ribonuclease enzyme that processes primary miRNA transcripts in the nucleus into precursor miRNAs.

Dicer:

An enzyme that further processes precursor miRNAs in the cytoplasm into mature miRNAs, which are then incorporated into RISC.

RNA-induced silencing complex (RISC): A multiprotein complex that mediates the silencing of target mRNAs through the action of bound miRNAs.