什么是 Regulated splicing？

Alternative splicing produces different messengers from one gene by exon skipping, the choice between mutually exclusive exons, the retention of an intron, or the use of alternative 5$'$ or 3$'$ splice sites. It is regulated by RNA-binding proteins that bind sequence elements in the exons and introns near a splice site: SR proteins bound to exonic enhancers recruit the spliceosome and promote inclusion of the exon, hnRNP proteins bound to silencers block it, and the outcome in a given cell is set by the relative amounts of the two kinds. More than $90\,\%$ of human multi-exon genes are alternatively spliced; the Dscam gene of Drosophila, with four blocks of mutually exclusive exons (12, 48, 33 and 2 alternatives), can produce $38\,016$ distinct proteins, each neuron expressing a different set that lets its branches recognise and avoid one another.