Fragile X syndrome (FXS) is a multi-organ disease that leads to mental retardation, macro-orchidism in males and premature ovarian insufficiency in female carriers. FXS is also a prominent monogenic disease associated with autism spectrum disorders (ASDs). FXS is typically caused by the loss of fragile X mental retardation 1 (FMR1) expression, which codes for the RNA-binding protein FMRP. Here we report the discovery of distinct RNA-recognition elements that correspond to the two independent RNA-binding domains of FMRP, in addition to the binding sites within the messenger RNA targets for wild-type and I304N mutant FMRP isoforms and the FMRP paralogues FXR1P and FXR2P (also known as FXR1 and FXR2). RNA-recognition-element frequency, ratio and distribution determine target mRNA association with FMRP. Among highly enriched targets, we identify many genes involved in ASD and show that FMRP affects their protein levels in human cell culture, mouse ovaries and human brain. Notably, we discovered that these targets are also dysregulated in Fmr1−/− mouse ovaries showing signs of premature follicular overdevelopment. These results indicate that FMRP targets share signalling pathways across different cellular contexts. As the importance of signalling pathways in both FXS and ASD is becoming increasingly apparent, our results provide a ranked list of genes as basis for the pursuit of new therapeutic targets for these neurological disorders. RNA-recognition elements are identified for the fragile-X-syndrome-associated RNA-binding protein FMRP, in addition to its target messenger RNAs; although many of FMRP gene targets discovered are involved in brain function and autism spectrum disorder, a proportion are also dysregulated in mouse ovaries, suggesting cross-regulation of signalling pathways in different tissues. Fragile X syndrome (FXS) is caused by mutations in the FMR1 gene, which encodes an RNA-binding protein called FMRP. This study from Thomas Tuschl's laboratory has now defined, on a genome-wide level, the targets bound by FMRP and by a disease-associated mutated version of FMRP. Although many of the top targets are involved in brain function and autism spectrum disorder, a surprising number of targets are also dysregulated in mouse ovaries, suggesting cross-regulation of signalling pathways in different tissues.

FMRP targets distinct mRNA sequence elements to regulate protein expression