Dicing Bodies

Abstract

In eukaryotes, small noncoding RNAs of approximately 21 to 24 nucleotides function as guide molecules in many biological processes, including genome organization and stability, developmental timing and patterning, and antibacterial and antiviral defense (Carrington and Ambros, 2003; Poethig, 2009; Simon and Meyers, 2011). The small RNAs regulate the functions of target DNA or RNA in a sequence-specific manner at either the transcriptional or posttranscriptional level through an RNA-silencing mechanism (Hammond, 2005; Czech and Hannon, 2011). Based on whether RNase III family proteins participate in the biogenesis, the small RNAs are divided into at least two classes: RNase III family protein-dependent small RNAs, including microRNAs (miRNAs) and many small interfering RNAs (siRNAs); and RNase III family protein-independent small RNAs, including Piwi-RNAs and secondary siRNAs that are processed from single-stranded precursors in worms (Czech and Hannon, 2011). The mature miRNAs and siRNAs are sorted and loaded specifically with Argonaute (AGO) subfamily proteins, forming the RNA-induced silencing complexes (RISCs) that undergo a specific RNA-silencing mechanism (Ender and Meister, 2010; Fabian et al., 2010). Here, we briefly summarize the molecular basis of miRNA biogenesis pathways and provide an update on nuclear dicing bodies (D-bodies), structures involved in miRNA processing in plant cells. For an overview on siRNAs and other small RNAs, readers are referred to recent excellent articles (Li et al., 2006; Pontes et al., 2006; Ahmad et al., 2010; Chen, 2010a; Law and Jacobsen, 2010; Czech and Hannon, 2011; Simon and Meyers, 2011; Zhang and Zhu, 2011).