Lin Shi-Lung, Chang Donald, Ying Shao-Yao
Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, 1333 San Pablo Street, BMT-403, Los Angeles, CA 90033, USA.
Gene. 2005 Aug 15;356:32-8. doi: 10.1016/j.gene.2005.04.036.
The two oligonucleotide strands of a siRNA duplex are functionally asymmetric in assembling the RNAi effector, RNA-induced gene silencing complex (RISC). Based on this asymmetric RISC assembly model in vitro, formation of a microRNA (miRNA) and complementary miRNA (miRNA*) duplex was proposed to be an essential step for the assembly of miRNA-associated RISC (miRISC). We observed here that a strong structural bias exists in the selection of a mature miRNA strand for RISC assembly in zebrafish using an intronic miRNA-like vector to target EGFP mRNA for regulation. The position of the stemloop in a precursor miRNA (pre-miRNA) was involved in the determination of miRNA-miRNA* asymmetry of the pre-miRNA stemarm, leading to different miRNA maturation during miRISC assembly. These findings suggest that the miRISC assembly is likely different from the RISC assembly model of siRNA in zebrafish, providing the first in vivo evidence for asymmetric miRISC assembly.
在组装RNAi效应物RNA诱导基因沉默复合体（RISC）的过程中，小干扰RNA（siRNA）双链体的两条寡核苷酸链在功能上是不对称的。基于体外这种不对称的RISC组装模型，有人提出微小RNA（miRNA）与互补微小RNA（miRNA*）双链体的形成是组装与miRNA相关的RISC（miRISC）的关键步骤。我们在此观察到，在斑马鱼中利用内含子miRNA样载体靶向EGFP mRNA进行调控时，在选择用于RISC组装的成熟miRNA链方面存在强烈的结构偏向性。前体miRNA（pre-miRNA）中茎环的位置参与了pre-miRNA茎臂的miRNA-miRNA*不对称性的确定，导致在miRISC组装过程中不同的miRNA成熟。这些发现表明，斑马鱼中的miRISC组装可能不同于siRNA的RISC组装模型，为不对称miRISC组装提供了首个体内证据。
