Mammalian Introns: When the Junk Generates Molecular Diversity

Abstract : Introns represent almost half of the human genome, yet their vast majority is eliminated from eukaryotic transcripts through RNA splicing. Nevertheless, they feature key elements and functions that deserve further interest. At the level of DNA, introns are genomic segments that can shelter independent transcription units for coding and non-coding RNAs which transcription may interfere with that of the host gene, and regulatory elements that can influence gene expression and splicing itself. From the RNA perspective, some introns can be subjected to alternative splicing. Intron retention appear to provide some plasticity to the nature of the protein produced, its distribution in a given cell type and timing of its translation. Intron retention may also serve as a switch to produce coding or non-coding RNAs from the same transcription unit. Conversely, splicing of introns has been directly implicated in the production of small regulatory RNAs. Hence, splicing of introns also appears to provide plasticity to the type of RNA produced from a genetic locus (coding, non-coding, short or long). We addressed these aspects to add to our understanding of mechanisms that control the fate of introns and could be instrumental in regulating genomic output and hence cell fate. 4430 In eukaryotes, the process of making a messenger RNA (mRNA) involves the co-transcriptional excision of introns in the nucleus, whereas joined-exons are exported to the cytoplasm to be translated. As a consequence, introns are inherently non-protein-coding sequences in that they are transcribed but not translated (usually) into protein. Because, and by definition, introns always lie between 2 exons, they were called "Intervening" or INtrons. By opposition, exons are those sequences that are EXpressed and EXported to the cytoplasm.
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Florent Hubé, Claire Francastel. Mammalian Introns: When the Junk Generates Molecular Diversity. International Journal of Molecular Sciences, MDPI, 2015, 16 (3), pp.4429-4452. ⟨10.3390/ijms16034429⟩. ⟨hal-02127272⟩

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