The RNA-binding protein FMRP facilitates the nuclear export of N6-methyladenosine-containing mRNAs

Abstract

N⁶-Methyladenosine (m⁶A) is the most abundant post-transcriptional mRNA modification in eukaryotes and exerts many of its effects on gene expression through reader proteins that bind specifically to m⁶A-containing transcripts. Fragile X mental retardation protein (FMRP), an RNA-binding protein, has previously been shown to affect the translation of target mRNAs and trafficking of mRNA granules. Loss of function of FMRP causes fragile X syndrome, the most common form of inherited intellectual disability in humans. Using HEK293T cells, siRNA-mediated gene knockdown, cytoplasmic and nuclear fractions, RNA-Seq, and LC-MS/MS analyses, we demonstrate here that FMRP binds directly to a collection of m⁶A sites on mRNAs. FMRP depletion increased mRNA m⁶A levels in the nucleus. Moreover, the abundance of FMRP targets in the cytoplasm relative to the nucleus was decreased in Fmr1-KO mice, an effect also observed in highly methylated genes. We conclude that FMRP may affect the nuclear export of m⁶A-modified RNA targets.

Keywords: FMRP; Fmr1 KO mice; N6-methyladenosine (m6A); RNA metabolism; RNA methylation; RNA-binding protein; fragile X mental retardation protein (FMRP); gene regulation; mouse; mouse brain; neurological disease; nuclear RNA; nuclear RNA export; post-transcriptional modification.