Small RNA World microRNAs(miRNAs) ECES458 FALL 2001 Student: Kai He Instructor: Dr. Sahinalp

imRNAs: A New Class of Small RNA Molecules siRNAs: small interfering RNAs stRNAs: small temporal RNAs

siRNAs Small interfering RNAs that have an integral role in the phenomenon of RNA interference(RNAi), a form of post-transcriptional gene silencing RNAi: 22 nt fragments, which bind to the complementary portion of the target mRNA and tag it for degradation siRNA: a role in conferring resistance and in preventing transcription

stRNAs Small RNAs refer to small temporal RNAs Including 22 nt, such as lin-4 and let-7 RNAs Role: the temporal regulation of Caenorhabditits elegans development, preventing translation of their target mRNAs by binding to the target’s complementary 3’ untranslated regions(UTRs) From 70 nt ssRNA(single-stranded RNA)

Dicer A RNaseIII, which cleaves double-stranded RNA into discrete sizes Involving generate siRNA Dicer homologs exist in many organisms including C.elegans, yeast and humans Roles: cause defeats in development and gene silencing

Small RNA Molecules Found in: – Drosophila – C.elegans – Hela cells Genes – Lin-4 – Let-7 Structures – Precursor RNA is folded into stem-loop Roles – Regulate translation – Modify mRNA stability

Identifying miRNA Using biochemical and bioinformatics approaches Using Dicer to produce siRNA and stRNA, and obtain ~22 nt with 5’ phosphate region and 3’ hydroxy region mRNAs, tRNAs, or rRNAs: degradation products - miRNAs

Charateristics of miRNAs Found: More than 100 new miRNAs From: Drosophila, C.elegans, Hela cells and so on Conservation: 15% of these miRNAs were conserved with 1-2 mismatched across worm, fly, and mammalian genomes Location: located at either the 3’ or 5’ region of a stem-loop within ~70 nt RNA precursor Expression pattern: varied and some were expressed in all cells and at all developmental stages and others had a more restricted spatial and temporal expression pattern Suggestions: – miRNA might be involved in post-transcriptional regulation of developmental genes

Problems Now we are not able to identify the miRNA targets by using an informatics approaches Why: maybe the entire miRNA does not have to be complementary to the target in order for binding to occur Questions: – What do these miRNAs do? – Are they involved in post-transcriptional gene regulation, if so, what are their target genes?