BIOL-L211 Lecture 27 Outline of Last Lecture I. The Splicing ReactionII. The SpliceosomeIII. Alternative SplicingOutline of Current Lecture I. Drosophila Dscam GeneII. mRNA ExportIII. Regulatory RNAsIV. miRNA PathwayCurrent LectureRNA Splicing II and Regulatory RNAsI. Drosophila Dscam GeneA. Dscam stands for "Down syndrome cell-adhesion molecule"1. mRNA that has 24 exons2. Four of those exons have multiple variantsa. Can be alternatively splicedb. Only one variant remains in the mature mRNA3. One gene can yield 38,016 different mature transcripts & proteins (isoforms)a. Note: each round of transcription will only yield one transcript/timeB. Dscam proteins form cell surface receptors for neurons1. Important in attracting and repelling advancing axonsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Neuron:a. Nerve cellb. Components: cell body (soma), axon, dendrites, terminal buttonsc. Responsible for processing and transmitting signals to other cellsd. These signals occur at synapsesi. Signal trajectory from an axon to the dendrite of another neuron3. Dscam Isoformsa. Allow neurons to distinguish between each otherb. If two isoforms are the same, they repelc. If two isoforms are different, they attract (opposites attract!)d. Allows formation of specific patterns of neuronal connectionsII. mRNA ExportA. Prior to export: mRNA is capped, spliced, and polyadenylatedB. Exported out of the nucleus, into the cytoplasm via a nuclear pore complex1. Export is an active process2. Only fully processed mRNA can be exportedC. Requirements for transport:1. Transcript must have an associated set of proteins2. Proteins must signal that mRNA has been processedIII. Regulatory RNAsA. Additional types of RNA1. Present in both prokaryotes and eukaryotes2. Can regulate transcription and translation3. Vary in length4. Non-codingB. RNA interference (RNAi)1. Small regulatory RNAs (such as siRNA and miRNA) can silence specific genesC. Small Interfering RNA (siRNA)1. Originates from long double stranded RNA2. Can be natural or artificial3. Processed into short fragments of dsRNA which is then processedD. MicroRNA (miRNA)1. Comes from transcribed RNA folding back on itself2. Is first processed into pri-miRNA and pre-miRNAIV. miRNA PathwayA. When gene for miRNA is transcribed, it mainly produces miRNA (pri-miRNA), which then folds back on itselfB. pri-miRNA is processed by Drosha before leaving the nucleus to make pre-miRNA1. Both Drosha and DGCR8 recognize pri-miRNA2. Drosha cleaves pri-miRNA3. Product of cleavage is the pre-miRNA stem loopC. pre-miRNA can then be exported to the cytoplasmD. A dicer cuts pre-miRNA and siRNA into short double-stranded fragmentsE. RNA-induced Silencing Component (RISC) associates with miRNA1. Binds one strand of a double stranded RNA fragment2. Central component is Argonaute3. miRNA considered mature after associationF. miRNA uses RNA-RNA base pairing to direct RISC to target
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