Nuclear Export of MicroRNA Precursors

Abstract

MicroRNAs (miRNAs), which function as regulators of gene expression in eukaryotes, are processed from larger transcripts by sequential action of nuclear and cytoplasmic ribonuclease III-like endonucleases. We show that Exportin-5 (Exp5) mediates efficient nuclear export of short miRNA precursors (pre-miRNAs) and that its depletion by RNA interference results in reduced miRNA levels. Exp5 binds correctly processed pre-miRNAs directly and specifically, in a Ran guanosine triphosphate-dependent manner, but interacts only weakly with extended pre-miRNAs that yield incorrect miRNAs when processed by Dicer in vitro. Thus, Exp5 is key to miRNA biogenesis and may help coordinate nuclear and cytoplasmic processing steps.

Principles of micro-RNA production and maturation

“…Once pre-miRNAs are produced, they are exported from the nucleus to the cytoplasm by Exportin5 (Exp5) and its Ran-guanosine triphosphate (GTP) cofactor (Figure 2a; Yi et al, 2003;Bohnsack et al, 2004;Lund et al, 2004). Exp5 is a member of the karyopherin family that mediates macromolecular nucleocytoplamic trafficking.…”

MiRNA expression analysis during normal zebrafish development and following inhibition of the Hedgehog and Notch signaling pathways

“…Approximately 50% are encoded within the introns of other genes (Rodriguez et al, 2004) whereas the remainder are synthesized as either mono-or poly-cistronic transcripts (Kim and Nam, 2006). Primary transcripts (primiRNAs) are first cleaved by the RNase III-like enzyme, Drosha, into ϳ70 nt hairpins (pre-miRNA) that are subsequently exported from the nucleus via Exportin 5 (Yi et al, 2003;Lund et al, 2004). Once in the cytoplasm, another RNase III enzyme, Dicer, cleaves pre-miRNAs into mature miRNA duplexes, one strand of which is then unwound and incorporated into RNA Induced Silencing Complexes (RISC), the formation of which appears to be linked to target identification and pairing (Gregory et al, 2005;Matranga et al, 2005;Rand et al, 2005).…”

FGF‐4 signaling is involved in mir‐206 expression in developing somites of chicken embryos

“…The Droshagenerated pre-miRNA is a 70-to 80-nt RNA with a typical stem-loop structure. It is transported to the cytoplasm by Exportin-5 (Yi et al, 2003;Lund et al, 2004) where it is processed by another RNaseIII type protein, Dicer, to generate the mature (20-to 22-nt) miRNA (Grishok et al, 2001;Hutvagner et al, 2001;Ketting et al, 2001;Knight and Bass, 2001). miRNAs have partially complementary sequences to certain mRNAs and guide a protein complex, RISC (RNA induced silencing complex), to the target mRNAs (Khvorova et al, 2003;Schwarz et al, 2003).…”