A novel fragile X syndrome mutation reveals a conserved role for the carboxy-terminus in FMRP localization and function.
Bottom Line: We find that this novel peptide encodes a functional nuclear localization signal (NLS) targeting the patient FMRP to the nucleolus in human cells.We also reveal an evolutionarily conserved nuclear export function associated with the endogenous C-terminus of FMRP.In vivo analyses in Drosophila demonstrate that a patient-mimetic mutation alters the localization and function of Dfmrp in neurons, leading to neomorphic neuronal phenotypes.
Affiliation: VIB Center for the Biology of Disease, VIB, Leuven, Belgium Center for Human Genetics, University of Leuven School of Medicine and University Hospitals Leuven, Leuven, Belgium Program in Molecular and Developmental Genetics, Doctoral School of Biomedical Sciences, University of Leuven, Leuven, Belgium.Show MeSH
Related in: MedlinePlus
Mentions: FMRP is a member of protein family known as the FXR protein family (Siomi et al, 1995; Zhang et al, 1995; Kirkpatrick et al, 2001). Although highly similar in their N-terminus, the C-terminus of the FXR protein family (Supplementary Fig S3) is not conserved at the sequence level (Kirkpatrick et al, 2001). We therefore wondered whether the effects of the mutation on the human protein are conserved in other FMRP homologs, or whether they are human specific. Therefore, we exploited the Drosophila melanogaster model, given its genetic tractability and success as a tool to study neurodevelopmental processes and related disorders (Okray & Hassan, 2013). The fruit fly has a single FMR1 homolog—dfmr1—that equally resembles human FMR1 and FXR genes at the amino acid level (Wan et al, 2000; Morales et al, 2002). Various morphological, molecular, and behavioral phenotypes relevant to dfmr1 protein function have been described in Drosophila (Zhang et al, 2001; Morales et al, 2002; Pan et al, 2004; Reeve et al, 2005; Bassell & Warren, 2008; McBride et al, 2012). We selected a well-characterized neuronal population termed the Lateral Neurons ventral (LNv)—the fly circadian pacemaker neurons—whose connectivity phenotype is strongly affected by Dfmrp activity (Reeve et al, 2005). Specifically, the overexpression of dfmr1 in a wild-type background causes a consistent phenotype where the terminal axonal branches of sLNv neurons collapse (Reeve et al, 2005, 2008) (Fig5A).
Affiliation: VIB Center for the Biology of Disease, VIB, Leuven, Belgium Center for Human Genetics, University of Leuven School of Medicine and University Hospitals Leuven, Leuven, Belgium Program in Molecular and Developmental Genetics, Doctoral School of Biomedical Sciences, University of Leuven, Leuven, Belgium.