Evolution and function of mRNA 5'spliced leader (SL) trans-splicing

本研究的目的是了解一个重要但不完全了解的基因表达机制- 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，是复杂生物体或细胞中大多数基因表达的重要步骤。然而，与传统的RNA剪接不同的是，在反式剪接中，两个完全独立的RNA分子的片段被连接在一起。传统的RNA剪接在复杂生物中是普遍存在的，但SL反式剪接虽然广泛存在，但并非在每个群体中都存在。这种分布表明，SL反式剪接要么在进化过程中独立出现过几次，要么在不同的进化过程中丢失过几次。这个研究项目的目标之一是确定这些假设场景中哪一个是正确的。这些研究将集中在包括人类在内的动物的主要分支上，因为，尽管人类和其他高等脊椎动物不进行SL反式剪接，但我们最近发现，SL反式剪接确实发生在我们最接近的非脊椎动物脊索动物亲戚——被囊动物身上。我们将评估SL反式剪接在脊椎动物/脊索动物的主要类群中的分布，以及与脊索动物一起构成后口动物主要分支的其他几个门的分布。结果将使我们能够确定SL反式剪接是在被囊动物中出现，还是在脊椎动物中消失。我们还将在被囊动物中开展实验研究，以阐明脊索动物反式剪接的遗传功能。本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有用的见解。

The goal of this research is to understand the evolution and function of an important but imperfectly-understood gene expression mechanism - SL trans-splicing. SL trans-splicing is a form of RNA splicing, which is an important step in the expression of most genes in complex organisms or cells. However, unlike conventional RNA splicing, which cuts out segments from a single RNA molecule and joins them back together, in trans-splicing segments of two entirely independent RNA molecules are joined together. Conventional RNA splicing is universal among complex organisms, but SL trans-splicing, though widespread, is not found in every group. The distribution indicates that SL trans-splicing either arose independently several times during evolution, or it has been lost several different times. One of the goals of this research program is to determine which of these hypothetical scenarios is correct. These studies will be focussed on the major branch of the animals that includes humans, because, although humans and other higher vertebrates do not carry out SL trans-splicing, we recently discovered that SL trans-splicing does occur in our closest non-vertebrate chordate relatives, the tunicates. We will assess the distribution of SL trans-splicing among the major groups of vertebrates/chordates, and also in several other phyla that, along with the chordates, make up the major animal division termed the deuterostomes. The results will enable us to determine whether SL trans-splicing arose within the tunicates, or was lost within the vertebrates. We will also carry out experimental studies in tunicates to clarify the genetic functions of trans-splicing in the chordates. The information from this research will provide useful 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.