Presentation on theme: "What is RNA splicing?. Genetic information is transferred from genes to the proteins they encode via a messenger RNA intermediate DNAGENE messenger RNA."— Presentation transcript:
What is RNA splicing?
Genetic information is transferred from genes to the proteins they encode via a messenger RNA intermediate DNAGENE messenger RNA (mRNA) protein transcription translation
Most genes have their protein-coding information interrupted by non-coding sequences called introns. The coding sequences are then called exons DNA GENE intron exon 1exon 2 transcription precursor-mRNA (pre-mRNA) intron
The intron is also present in the RNA copy of the gene and must be removed by a process called RNA splicing protein translation mRNA RNA splicing pre-mRNA intron
Splicing a pre-mRNA involves two reactions pre-mRNA intron branchpoint A spliced mRNA Step 2 intermediates Step 1 A
Splicing occurs in a spliceosome an RNA-protein complex (simplified) pre-mRNAspliced mRNA spliceosome (~100 proteins + 5 small RNAs) Splicing works similarly in different organisms, for example in yeast, flies, worms, plants and animals.
RNA is produced in the nucleus of the cell. The mRNA has to be transported to the cytoplasm to produce proteins Ribosomes are RNA-protein machines that make proteins, translating the coding information in the mRNA
Pre-messenger RNA Processing cytoplasm nucleus mRNA RNA splicing M7 G AAAAAAA 200 pre-mRNA intron exon AAAAAAA 200 M7 G transport M7 G AAAAAAA 200 ribosomes protein cap poly(A) tail
Alternative splicing In humans, many genes contain multiple introns intron 2 intron 3 intron 4intron 1 Usually all introns must be removed before the mRNA can be translated to produce protein
However, multiple introns may be spliced differently in different circumstances, for example in different tissues Heart muscle mRNA 1435 Uterine muscle mRNA Thus one gene can encode more than one protein. The proteins are similar but not identical and may have distinct properties. This is important in complex organisms pre-mRNA
Different signals in the pre-mRNA and different proteins cause spliceosomes to form in particular positions to give alternative splicing We are studying how mRNAs and proteins interact in order to understand how these machines work in general and, in particular, how RNA splicing is regulated as it affects which proteins are produced in each cell and tissue in the body.
Fas pre-mRNA APOPTOSIS Alternative splicing can generate mRNAs encoding proteins with different, even opposite functions (programmed cell death) Fas ligand Soluble Fas (membrane) Fas Fas ligand (membrane- associated) (+) (-)
Alternative splicing can generate tens of thousands of mRNAs from a single primary transcript Combinatorial selection of one exon at each of four variable regions generates more than 38,000 different mRNAs and proteins in the Drosophila cell adhesion molecule Dscam The protein variants are important for wiring of the nervous system and for immune response protein mRNA pre-mRNA
Examples of the potential consequences of mutations on splicing AB C Mutations occur on the DNA (in a gene) 12 mutation A truncated mRNA 5412 mutation B exon 3 skipped mutation C longer exon no mutation normal mRNA normal protein active truncated protein inactive protein of different size (smaller or longer) inactive or aberrant function
Pathologies resulting from aberrant splicing can be grouped in two major categories Mutations affecting proteins that are involved in splicing Examples:Spinal Muscular Atrophy Retinitis Pigmentosa Myotonic Dystrophy Mutations affecting a specific messenger RNA and disturbing its normal splicing pattern Examples:ß-Thalassemia Duchenne Muscular Dystrophy Cystic Fibrosis Frasier Syndrome Frontotemporal Dementia and Parkinsonism
Therefore, understanding the mechanism of RNA splicing in normal cells and how it is regulated in different tissues and at different stages of development of an organism is essential in order to develop strategies to correct aberrant splicing in human pathologies