The FMRP protein has been studied for its role in neuronal function and neurologic disease, and has paralleled our studies of the related neuron-specific RNA binding protein Nova. Both proteins harbor two tandem KH-type RNA binding domains, a spacer region, and a third RNA binding domain, which is an RGG-box (Reviewed in: Burd CG, Dreyfuss G. Science. 1994 Jul 29;265(5172):615-21. Review) in the case of FMRP.
RNA selection studies with full-length FMRP yielded a high affinity structure and sequence-specific RNA target termed a G-quartet ( Darnell JC, Jensen KB, Brown V, Jin P, Warren ST and Darnell RB. Cell, 107:489-499, 2001. See minireview Kaytor & Orr, Cell 107:555-7, 2001] ). This RNA motif has been used to try and sort through candidate target RNAs and identify those RNAs regulated by FMRP (Brown V, Ceman S, Jin P, Darnell JC, O'Donnell WT, Tenenbaum SA,Wilkinson KD, Keene JD, Darnell RB and Warren ST. Cell, 107:477-487, 2001.)
More recently, we have studied RNAs specifically targeted by the FMRP KH2 domain. This work has been driven in part by reports of a severely affected patient harboring a mutation (I304N; DeBoulle K et al., Nat Genet, 3:31-35, 1993) in FMRP KH2. These studies have identified a new type of RNA target that appears to be relevant to FMRP biology (Darnell JC, Fraser CE, Mostovetsky O, Stefani G, Jones TA, Eddy SR, Darnell RB. Genes Dev. 2005 Apr 15;19 (8):903-18).
We have related FMRP biology to translation in neurons. We have developed a method to reliably produce high quality polysomes from mouse brain (Stefani G, Fraser CE, Darnell JC and Darnell RB. J Neurosci. 2004 Aug 18;24(33):7272-6). We see evidence in a neuronal cell line that FMRP is associated with functional, actively translating (puromycin-sensitive) polysomes.
Ongoing projects in the lab include using CLIP analysis to identify FMRP RNA targets, and efforts to relate FMRP RNA targets to the function of the protein.