Non-coding RNAs

percentages of RNA in eukaryotic cells

~4-8% mRNA, lncRNA

~12-18% tRNA, miRNA

~2-6% snoRNA

~75-85% rRNA and snRNA

miRNA functions

enhance or activate translation of certain mRNAs (interact with 5’ UTR facilitating recruitment by ribosome)

inhibit translation (interact with 3’ region of mRNA, blocking translation and inducing degradation of transcript)

mediators of intercellular signaling (secreted and bind to receptors located on specific cell types, eliciting response)

lncRNA

long, non-coding, a large and highly diverse class of ncRNAs that are >200 nt in length

can be transcribed in sense or antisense directions from various genomic regions, including introns or exons of overlapping protein-coding genes, intergenic regions (lincRNAs), telomeres, centromeric repeats, ribosomal DNA loci, promotrs, enhancers, UTRs, or just random parts of the genome

often show high tissue specificity and their expression alters dynamically during development

how do lncRNAs regulate gene expression?

interacting with DNA at enhancers or promoters, activating or suppressing their function

interacting and forming complexes with proteins

interacting with various other RNAs, including mRNAs, snRNAs, miRNAs

interacting with proteins, can serve as scaffolds or guides to promote co-localization of proteins or facilitate protein-protein interactions

lncRNAs can affect

viability, immune system, genome stability/aging, limb development, infertility, brain development, dosage compensation/growth

lncRNAs can have complex

gene architecture, similar to protein coding genes

lncRNAs share same mechanisms of

transcription and processing (RNA pol II, 5’ cap, polyA tail, spliceosomal processing)

lncRNA domain modularity

contributes to expand variety of functions

circular RNAs (circRNAs)

new players in gene regulation

RNA splicing can generate these containing exons, introns, or both

thought to be largely aberrant products of splicing but in some cases acquire important roles (many unknown)

interact with other molecules (RNA, proteins) in similar ways as other non-coding RNAs