The nuclear export receptor XPO-1 supports primary miRNA processing in C. elegans and Drosophila

Eric C Lai,Ingo Büssing,Jr-Shiuan Yang,Helge Großhans

doi:10.1038/emboj.2010.82

Abstract

MicroRNA (miRNA) biogenesis proceeds from a primary transcript (pri-miRNA) through the pre-miRNA into the mature miRNA. Here, we identify a role of the Caenorhabditis elegans nuclear export receptor XPO-1 and the cap-binding proteins CBP-20/NCBP-2 and CBP-80/NCBP-1 in this process. The RNA-mediated interference of any of these genes causes retarded heterochronic phenotypes similar to those observed for animals with mutations in the let-7 miRNA or core miRNA machinery genes. Moreover, pre- and mature miRNAs become depleted, whereas primary miRNA transcripts accumulate. An involvement of XPO-1 in miRNA biogenesis is conserved in Drosophila, in which knockdown of Embargoed/XPO-1 or its chemical inhibition through leptomycin B causes pri-miRNA accumulation. Our findings demonstrate that XPO-1/Emb promotes the pri-miRNA-to-pre-miRNA processing and we propose that this function involves intranuclear transport and/or nuclear export of primary miRNAs.

Highlights

According to the current model of miRNA biogenesis, miRNAs are transcribed by RNA polymerase II as capped and polyadenylated primary miRNAs of several hundred or thousands of nucleotides in length (Bracht et al, 2004; Cai et al, 2004; Lee et al, 2004)
Results xpo-1 is a heterochronic gene in C. elegans Exp5 is a member of the importin b-superfamily that mediates the nuclear export of pre-miRNAs in flies and & 2010 European Molecular Biology Organization
The exportin XPO-1 is the orthologue of yeast and human CRM1/XPO1, which mediates nuclear export of the spliceosomal U snRNAs (Hutten and Kehlenbach, 2007), whereas XPO-3 is the orthologue of human Exportin-t and yeast Los1p, which mediates tRNA nuclear export (Grohans et al, 2000). xpo-1 has previously been identified as one among 4200 genes, depletion of which enhanced vulval bursting for a weak let-7 allele in an RNAi-sensitized, eri-1 mutant background, a function in miRNA biogenesis remained elusive (Parry et al, 2007)

Summary

Introduction

According to the current model of miRNA biogenesis, miRNAs are transcribed by RNA polymerase II as capped and polyadenylated primary miRNAs (pri-miRNA) of several hundred or thousands of nucleotides in length (Bracht et al, 2004; Cai et al, 2004; Lee et al, 2004). The depletion of several components of the miRNA core machinery in C. elegans results in developmental phenotypes that resemble those seen upon the loss of the let-7 miRNA, such that these phenotypes provided the first indication for a function of DCR-1, ALG-1/2, and AIN-1/2 in the miRNA pathway (Grishok et al, 2001; Ketting et al, 2001; Ding et al, 2005; Zhang et al, 2007) These so-called heterochronic phenotypes are apparent in a subset of skin cells, the seam cells. On more complete loss of let-7 or general miRNA activity, animals die by vulval bursting at the L/A transition

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Conclusion