Pre-miRNA

Definition

Pre-miRNA, or precursor microRNA, is a short, hairpin-shaped RNA molecule that serves as an intermediate form in the biogenesis of microRNAs. It is synthesized in the nucleus from primary miRNA (pri-miRNA) transcripts and is essential for the subsequent processing into mature miRNA, which plays a key role in post-transcriptional regulation of gene expression.

5 Must Know Facts For Your Next Test

1. Pre-miRNAs are typically 70-100 nucleotides in length and contain a double-stranded region formed by base-pairing of complementary sequences.
2. The export of pre-miRNAs from the nucleus to the cytoplasm is facilitated by exportin-5, which recognizes their specific structure.
3. Once in the cytoplasm, pre-miRNAs are processed by Dicer to generate mature miRNAs, which are then incorporated into RISC for gene regulation.
4. The accurate processing of pre-miRNAs is crucial for the generation of functional miRNAs, and any errors can lead to misregulation of gene expression.
5. Pre-miRNAs are involved in various biological processes, including development, differentiation, and responses to environmental stress.

Review Questions

• How is pre-miRNA generated from pri-miRNA and what role does it play in the overall miRNA biogenesis pathway?
  • Pre-miRNA is generated from pri-miRNA through a process involving the enzyme Drosha, which cleaves the primary transcript into shorter hairpin structures. This step is crucial because pre-miRNAs serve as intermediates that are then exported from the nucleus and further processed into mature miRNAs by Dicer. The production of functional miRNAs from pre-miRNAs is essential for regulating gene expression and maintaining cellular homeostasis.
• Discuss the significance of Dicer in the processing of pre-miRNA and how this impacts miRNA function.
  • Dicer plays a vital role in converting pre-miRNAs into mature miRNAs by cleaving their hairpin structures. This enzyme ensures that pre-miRNAs are processed accurately, generating double-stranded RNA that can be loaded into RISC. If Dicer malfunctions or if there are issues with pre-miRNA processing, it can lead to a decrease in functional miRNAs, thereby disrupting regulatory pathways and potentially resulting in diseases such as cancer.
• Evaluate the implications of dysregulated pre-miRNA processing on cellular functions and potential disease states.
  • Dysregulated processing of pre-miRNAs can lead to altered levels of mature miRNAs, which may disrupt normal gene regulation and contribute to various disease states. For instance, improper processing may result in insufficient suppression of oncogenes or failure to regulate tumor suppressor genes, promoting cancer progression. Furthermore, this dysregulation can affect developmental processes and cellular responses to stress, showcasing the critical importance of precise pre-miRNA processing in maintaining cellular health and function.

Related terms

miRNA: MicroRNA (miRNA) is a small non-coding RNA molecule that regulates gene expression by binding to complementary sequences on target mRNAs, leading to their degradation or inhibition of translation.

Dicer: Dicer is an enzyme that processes pre-miRNA into mature miRNA by cleaving the hairpin structure, resulting in a double-stranded RNA molecule that can be incorporated into the RNA-induced silencing complex (RISC).

pri-miRNA: Primary microRNA (pri-miRNA) is the initial transcript that is processed into pre-miRNA; it contains one or more hairpin structures and is usually several hundred to thousands of nucleotides long.