Muro A F, Iaconcig A, Baralle F E
International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
FEBS Lett. 1998 Oct 16;437(1-2):137-41. doi: 10.1016/s0014-5793(98)01201-0.
Alternatively spliced exons generally contain weak splicing sites, and exonic and/or intronic regulatory elements recognised by trans-acting auxiliary splicing factors. The EDA exon of the fibronectin gene is a typical example of an exon bearing a purine-rich exon splicing enhancer (ESE) element recognised by members of the SR phosphoprotein family. The regulatory region that governs splicing in the human EDA exon also contains an exon splicing silencer (ESS) element. We have cloned the mouse EDA genomic region, and we show that the ESE and the ESS elements, although they have base differences, can be replaced by the human elements without significant change in the exon inclusion/exclusion ratio. This fact suggests a common splicing regulatory mechanism across species. We demonstrate in vivo the functional activity of the mouse ESE element in splicing. We also show that the trans-acting factors recognising this element cooperate with the 5' splicing site of the EDA exon to facilitate proper exon recognition. Indeed, a strong 5' splicing site overrides the ESE function in exon recognition. However, the presence of a strong 3' splicing site is not sufficient to compensate for the absence of the splicing enhancer. Our data provide in vivo evidence of the interplay between the exonic splicing regulatory elements and the splicing sites, leading finally to subtle regulation of alternative splicing.
可变剪接外显子通常含有较弱的剪接位点，以及可被反式作用辅助剪接因子识别的外显子和/或内含子调控元件。纤连蛋白基因的EDA外显子就是一个典型例子，该外显子带有一个富含嘌呤的外显子剪接增强子（ESE）元件，可被SR磷蛋白家族成员识别。在人类EDA外显子中控制剪接的调控区域还包含一个外显子剪接沉默子（ESS）元件。我们克隆了小鼠EDA基因组区域，并且发现，尽管ESE和ESS元件存在碱基差异，但它们可被人类元件替代，而外显子包含/排除比率没有显著变化。这一事实表明不同物种间存在共同的剪接调控机制。我们在体内证明了小鼠ESE元件在剪接中的功能活性。我们还表明，识别该元件的反式作用因子与EDA外显子的5'剪接位点协同作用，以促进正确的外显子识别。实际上，一个强的5'剪接位点在外显子识别中会优先于ESE功能。然而，一个强的3'剪接位点的存在并不足以弥补剪接增强子的缺失。我们的数据提供了体内证据，证明外显子剪接调控元件与剪接位点之间存在相互作用，最终导致可变剪接的精细调控。
