Testing the Reverse-splicing Model of Intron Spread with rDNA Genes

爱荷华州大学的Deepenish Bhattacharya博士获得了一笔资助，以确定插入序列（所谓的“内含子”）是如何传播到基因中的新位点的。 内含子构成基因组的重要组成部分（约占人类基因组的16%），在基因表达和疾病中发挥重要作用，但其传播方式仍不清楚。 这是因为很少有证明最近和广泛的内含子传播的情况下已被记录。 在真子囊菌纲真菌的核糖体（r）RNA基因中发现了大量新近插入的内含子，这使得真子囊菌成为研究内含子扩散的理想材料。 先前的工作表明，内含子被整合到基因中的机制的一个很好的候选者是剪接过程的逆转。 将研究不同真子囊菌群的rRNA，以测试“反向剪接”模型的预测，例如期望内含子优先保留在对剪接因子具有高亲和力的靶基因序列处，并且内含子是非随机分布的，其中大多数聚集在未被掩埋在RNA三级结构中的区域中。 内含子在真核生物基因组的进化过程中起着重要的作用，并与疾病有关。 例如，约15%与人类遗传疾病相关的点突变会导致内含子剪接缺陷。 因此，令人惊讶的是，不存在内含子扩散的一般模型。 在这项资助中，最近发现的广泛的内含子在真子囊菌纲真菌的核rDNA被利用来解决内含子传播的问题。 真菌系统的一个重要优势是强大的二级和三级rRNA结构的可用性。这允许测试RNA结构在确定内含子分布中的作用，这是不能用大多数前mRNA进行的分析，因为前mRNA具有很大程度上未知的折叠特性。

A grant has been awarded to Dr. Debashish Bhattacharya at the University of Iowa to determine how intervening sequences (so-called "introns") spread into novel sites in genes. Introns compose a significant portion of genomes (about 16% in humans) and play important roles in gene expression and disease, yet their means of spread remains unknown. This is because few proven cases of recent and widespread intron spread have been documented. The finding of a wealth of recently inserted introns in the ribosomal (r)RNA genes of Euascomycetes fungi makes these organisms ideal for the study of intron spread. Previous work shows that a good candidate for the mechanism by which introns get incorporated into genes is by reversal of the splicing process. The rRNAs of a diverse group of Euascomycetes will be studied to test predictions of the "reverse-splicing" model such as the expectation that introns are preferentially retained at target gene sequences that have a high affinity for splicing factors and that introns are non-randomly distributed, with most of them clustering in regions that are not buried in RNA tertiary structure. Introns play important roles in the evolution of eukaryotic genomes and are implicated in diseases. For example, about 15% of point mutations that are linked to human genetic disease cause defects in the splicing of introns. It is surprising, therefore, that no general model of intron spread exists. In this grant, the recent finding of widespread introns in the nuclear rDNA of Euascomycetes fungi is exploited to address the issue of intron spread. An important strength of the fungal system is the availability of robust secondary and tertiary rRNA structures. This allows the testing of the role of RNA structure in determining intron distribution, an analysis that cannot be done with most pre-mRNAs which have largely unknown folding properties.