Purification of dFMR1-containing complexes using tandem affinity purification.

Fragile X syndrome results from the lack of FMR1 expression. To understand how the lack of FMR1 function leads to the syndrome, we are studying the Drosophila FMR1 related protein (dFMR1). We performed affinity purification of dFMR1-associated complexes from cultured Drosophila S2 cells and found that dFMR1 associates with a key component of RNA interference, AGO2. Our finding suggests cross talk between the fragile X syndrome protein and RNA interference. In this chapter, we describe a tandem affinity purification method to isolate the protein components and small RNAs in the dFMR1-associated complexes.

Roles of R2D2, a cytoplasmic D2 body component, in the endogenous siRNA pathway in Drosophila.

Endogenous small interfering RNAs (endo-siRNAs) in Drosophila are processed by Dicer-2 (Dcr-2) and loaded onto Ago2 by the Dcr-2/R2D2 heterodimer. In r2d2 mutants, the level of endo-siRNAs is unchanged, but endo-siRNAs are misloaded onto Ago1. However, the mechanism underlying the control of endo-siRNA sorting by R2D2 remains unknown. Here, we show that R2D2 controls endo-siRNA sorting by localizing Dcr-2, and presumably endo-siRNA duplexes, to cytoplasmic foci, D2 bodies. Ago2, but not Ago1, localized to D2 bodies. dsRNA-binding-deficient mutant, but not wild-type, R2D2 failed to localize D2 bodies and caused endo-siRNA misdirection to Ago1 in R2D2-depleted cells. However, R2D2 was dispensable for sorting miRNAs and exogenous siRNAs onto Ago1 and Ago2, respectively, in vivo. Endo- and exo-siRNA guide selection also occurred R2D2 independently. The functions of R2D2 are required to avoid endo-siRNA misdirection to Ago1, because Ago1 is capable of loading incompletely complementary miRNA duplexes and endo-siRNA duplexes.