Evolution and function of spliced leader (SL) trans-splicing in the chordates and deuterostomes

本研究的目的是了解一个鲜为人知的基因表达机制- SL反式剪接的进化和功能。SL反式剪接是RNA剪接的一种形式，这是一种复杂的机制，在复杂细胞和生物体中的大多数基因表达中起关键作用。然而，与传统的RNA剪接不同，它切割单个RNA分子的片段并将它们连接在一起，反式剪接涉及两个完全独立的RNA分子的切割和连接。常规剪接在复杂生物体中是普遍的，但SL反式剪接不是。有些人这样做，有些人不这样做。SL反式剪接在动物生命进化树中的分布是零星的。这种分布表明，SL反式剪接是一种古老的机制，在许多群体中已经丢失，或者它是一种在动物进化过程中独立出现的机制。这项研究的目标之一是确定哪些进化假说是正确的。我们的研究集中在动物进化树的划分上，后口动物，包括我们的门-脊索动物，以及我们在脊索动物中的特殊群体-脊椎动物。脊椎动物，如哺乳动物或鸟类不做SL反式剪接，但我们最近发现SL反式剪接在一个简单的脊索动物组，被囊动物。我们将确定是否其他后口动物和脊索动物组除了被囊动物进行反式剪接。这种模式将揭示反式剪接是在被囊动物中发明的，还是在脊椎动物中丢失的。我们还将在被囊动物中进行实验研究，以阐明反式剪接的遗传功能。这项研究的信息将为基因表达机制的进化动力学以及基因表达机制的进化变化对基因组进化的影响提供新的见解。

The goal of this research is to understand the evolution and function of a poorly understood gene expression mechanism - SL trans-splicing. SL trans-splicing is a form of RNA splicing, a complex mechanism that plays a key role in the expression of most genes in complex cells and organisms. However unlike conventional RNA splicing, which cuts out segments of a single RNA molecule and joins them together, trans-splicing involves the cutting and joining of two entirely independent RNA molecules. Conventional splicing is universal among complex organisms, but SL trans-splicing is not. Some groups do it, and some groups don't. The distribution of SL trans-splicing in the evolutionary tree of animal life is sporadic. This distribution indicates that either SL trans-splicing is an ancient mechanism that has been lost in many groups, or it is a mechanism that has arisen independenly several different times during animal evolution. One of the goals of this research is to establish which of those evolutionary hypotheses is correct. Our studies are focused on the division of the animal evolutionary tree, the deuterostomes, that includes our phylum - the chordates, and our particular group within the chordates - the vertebrates. Vertebrates such as mammals or birds do not do SL trans-splicing, but we recently discovered SL trans-splicing in a simple chordate group, the tunicates. We will determine whether other deuterostome and chordate groups apart from the tunicates carry out trans-splicing. The pattern will reveal whether trans-splicing was invented in the tunicates, or lost in the vertebrates. We will also carry out experimental studies in tunicates to clarify the genetic functions of trans-splicing. The information from this research will provide novel insight into the evolutionary dynamics of gene expression mechanisms and on the impact of evolutionary change in gene expression mechanisms on the evolution of the genome.