Small non-coding RNAs (sncRNAs) are a diverse class of RNA molecules that are relatively short in length and do not code for proteins. They are essential players in various cellular processes and have been extensively studied in recent years due to their regulatory roles in gene expression and their significance in numerous biological functions.
The major types of small non-coding RNAs include:
MicroRNAs (miRNAs): miRNAs are short RNA molecules typically around 22 nucleotides in length. They regulate gene expression post-transcriptionally by binding to specific messenger RNA (mRNA) molecules, leading to mRNA degradation or translational repression. miRNAs play crucial roles in developmental processes, cell differentiation, and response to environmental changes.
Small Interfering RNAs (siRNAs): siRNAs are double-stranded RNA molecules, usually 21-23 nucleotides long, that are involved in RNA interference (RNAi) pathways. They mediate the degradation of target mRNA molecules with complementary sequences, leading to gene silencing.
PIWI-interacting RNAs (piRNAs): piRNAs are typically longer, around 24-31 nucleotides, and interact with PIWI proteins to form complexes that are involved in protecting the genome from transposable elements (TEs) or “jumping genes.” piRNAs are mainly expressed in germ cells and are essential for maintaining genome integrity in the germline.
Small Nucleolar RNAs (snoRNAs): snoRNAs are involved in the modification and processing of ribosomal RNA (rRNA) and transfer RNA (tRNA) molecules, ensuring their proper functioning during translation.
Small Nuclear RNAs (snRNAs): snRNAs are involved in splicing pre-mRNA molecules, a process known as pre-mRNA splicing, which is necessary for removing introns and joining exons to generate mature mRNA.
Small Cajal Body-specific RNAs (scaRNAs): scaRNAs are involved in the post-transcriptional modification of snRNAs and snoRNAs.
Y RNAs: Y RNAs are small non-coding RNAs that associate with Ro60 protein to form Ro ribonucleoprotein (Ro RNP) complexes. They have diverse roles in RNA metabolism and are involved in RNA quality control.
Vault RNAs (vtRNAs): Vaults are large ribonucleoprotein complexes involved in various cellular processes, and vtRNAs are small non-coding RNAs found within these complexes. Their exact functions are not fully understood.
Small non-coding RNAs play crucial roles in gene regulation, genome stability, epigenetic modifications, and cellular homeostasis. Dysregulation of these sncRNAs has been linked to various diseases, including cancer, neurodegenerative disorders, and metabolic disorders, making them important targets for further research and potential therapeutic interventions.