Neuronal Ceroid Lipofuscinoses (NCL) are a group of inherited neurodegenerative disorders with lysosomal pathology (CLN1-14). Recently, mutations in the DNAJC5/CLN4 gene, which encodes the presynaptic co-chaperone CSP were shown to cause autosomal-dominant NCL. Although 14 NCL genes have been identified, it is unknown if they act in common disease pathways. Here we show that two disease-associated proteins, CSPα and the depalmitoylating enzyme palmitoyl-protein thioesterase 1 (PPT1/CLN1) are biochemically linked. We find that in DNAJC5/CLN4 patient brains, PPT1 is massively increased and mis-localized. Surprisingly, the specific enzymatic activity of PPT1 is dramatically reduced. Notably, we demonstrate that CSP is depalmitoylated by PPT1 and hence its substrate. To determine the consequences of PPT1 accumulation, we compared the palmitomes from control and DNAJC5/CLN4 patient brains by quantitative proteomics. We discovered global changes in protein palmitoylation, mainly involving lysosomal and synaptic proteins. Our findings establish a functional link between two forms of NCL and serve as a springboard for investigations of NCL disease pathways.

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BackgroundThe Neuronal Ceroid Lipofuscinoses (NCL) comprise at least nine progressive neurodegenerative genetic disorders. Kufs disease, an adult-onset form of NCL may be recessively or dominantly inherited. Our study aimed to identify genetic mutations associated with autosomal dominant Kufs disease (ADKD).Methodology and Principal FindingsWe have studied the family first reported with this phenotype in the 1970s, the Parry family. The proband had progressive psychiatric manifestations, seizures and cognitive decline starting in her mid 20 s. Similarly affected relatives were observed in seven generations. Several of the affected individuals had post-mortem neuropathological brain study confirmatory for NCL disease. We conducted whole exome sequencing of three affected family members and identified a pLeu116del mutation in the gene DNAJC5, which segregated with the disease phenotype. An additional eight unrelated affected individuals with documented autosomal dominant or sporadic inheritance were studied. All had diagnostic confirmation with neuropathological studies of brain tissue. Among them we identified an additional individual with a p.Leu115Arg mutation in DNAJC5. In addition, a pAsn477Ser change in the neighboring gene PRPF6, a gene previously found to be associated with retinitis pigmentosa, segregated with the ADKD phenotype. Interestingly, two individuals of the Parry family did report visual impairment.ConclusionsOur study confirmed the recently reported association of DNAJC5 mutations with ADKD in two out of nine well-defined families. Sequence changes in PRPF6 have not been identified in other unrelated cases. The association of vision impairment with the expected PRPF6 dysfunction remains possible but would need further clinical studies in order to confirm the co-segregation of the visual impairment with this sequence change.

Loss of the RNA-binding protein FMRP (fragile X mental retardation protein) leads to fragile X syndrome, the most common form of inherited mental retardation. Although some of the messenger RNA targets of this protein, including FMR1, have been ascertained, many have yet to be identified. We have found that Xenopus elongation factor 1A (EF-1A) mRNA binds tightly to recombinant human FMRP in vitro. Binding depended on protein determinants located primarily in the C-terminal end of hFMRP, but the hnRNP K homology domain influenced binding as well. When hFMRP was expressed in cultured cells, it dramatically reduced endogenous EF-1A protein expression but had no effect on EF-1A mRNA levels. In contrast, the translation of several other mRNAs, including those coding for dynamin and constitutive heat shock 70 protein, was not affected by the hFMRP expression. Most importantly, EF-1A mRNA and hFMR1 mRNA were coimmunoprecipitated with hFMRP. Finally, in fragile X lymphoblastoid cells in which hFMRP is absent, human EF-1A protein but not its corresponding mRNA is elevated compared with normal lymphoblastoid cells. These data suggest that hFMRP binds to EF-1A mRNA and also strongly argue that FMRP negatively regulates EF-1A expression in vivo.The loss of a normal cellular protein, FMRP, 1 causes fragile X syndrome, one of the most common forms of mental retardation (MR). FMRP is a RNA-binding protein that contains two hnRNP K-homology (KH) binding domains and an arginineglycine-rich region that resembles an RGG box (1, 2). Several studies indicate that both the KH 2 domain and the arginineglycine-rich region likely play a role in RNA binding (1, 3-6), the latter interaction being mediated by a G quartet (7). FMRP associates with polyribosomes via a mRNP particle (8, 9), and it has been proposed to regulate gene expression post-transcriptionally (5, 10 -14). Mammalian FMRPs inhibit mRNA translation in vitro at nanomolar concentrations in both rabbit reticulocyte lysates (15) and in microinjected Xenopus oocytes (16). These data suggest that translational repression may be an in vivo function of FMRP. Indeed, the Drosophila homolog of FMRP, dFMR1, was found to bind and negatively regulate futsch mRNA (17).Recent studies have begun to delineate the mRNAs that mammalian FMRPs interact with in vivo. These studies have taken one of two forms. On the one hand, potential FMRP target mRNAs have been identified solely on the basis of their ability to bind to purified recombinant FMRP (15, 16) or cellfree produced FMRP (1, 3). Notwithstanding, it has not been determined whether any of these mRNAs bind to FMRP in vivo. On the other hand, mRNAs, including FMR1 mRNA, which associate with FMRP-containing mRNPs have also been isolated from cultured cells (10, 18). However, although these messages require FMRP in the mRNP for their association, it has not been demonstrated that they bind solely to it. Using the former methodology, we isolated a subset of mRNAs derived from normal adult brain that bind human FMRP (hFMRP) in vitro (3). Duri...

The fragile X mental retardation protein (FMRP), the functional absence of which causes fragile X syndrome, is an RNA-binding protein that has been implicated in the regulation of local protein synthesis at the synapse. The mechanism of FMRP's interaction with its target mRNAs, however, has remained controversial. In one model, it has been proposed that BC1 RNA, a small nonprotein-coding RNA that localizes to synaptodendritic domains, operates as a requisite adaptor by specifically binding to both FMRP and, via direct base-pairing, to FMRP target mRNAs. Other models posit that FMRP interacts with its target mRNAs directly, i.e., in a BC1-independent manner. Here five laboratories independently set out to test the BC1-FMRP model. We report that specific BC1-FMRP interactions could be documented neither in vitro nor in vivo. Interactions between BC1 RNA and FMRP target mRNAs were determined to be of a nonspecific nature. Significantly, the association of FMRP with bona fide target mRNAs was independent of the presence of BC1 RNA in vivo. The combined experimental evidence is discordant with a proposed scenario in which BC1 RNA acts as a bridge between FMRP and its target mRNAs and rather supports a model in which BC1 RNA and FMRP are translational repressors that operate independently.fragile X syndrome ͉ non-protein-coding RNAs ͉ translational control S mall non-protein-coding RNAs perform important functions in the regulation of eukaryotic gene expression (1). In the mammalian central nervous system, they have been implicated in promoting organism-environment interactions (2). Small untranslated BC1 RNA is a translational repressor that is thought to participate in the regulation of local protein synthesis at the synapse (2, 3). BC1 RNA represses translation by targeting assembly of 48S initiation complexes (4). Interacting with eukaryotic initiation factor 4A (eIF4A) and poly(A) binding protein (PABP) (4-6), BC1 RNA prevents recruitment of the 43S preinitiation complex to the mRNA. Targets of BC1-mediated repression are those mRNAs that depend on the eIF4 family of factors for efficient initiation (4).Fragile X syndrome is caused by the functional absence of fragile X mental retardation protein (FMRP) (7,8). Consensus has developed over recent years that FMRP is, like BC1 RNA, a translational repressor that is active in postsynaptic microdomains (7, 9, 10). However, in contrast to BC1 RNA, FMRP is associated with polysomes (11-15), indicating that BC1 RNA and FMRP operate at different levels in the translation pathway.In an alternative model, it has been proposed that BC1 RNA and FMRP interact directly with each other (16,17). In this scenario, BC1 RNA (i) physically binds to FMRP, (ii) directly interacts, by base-pairing of its 5Ј domain, with select mRNAs that are FMRP targets, and (iii) acts as a bridge between FMRP and such target mRNAs, thus serving as a requisite adaptor (16, 17).The above two models cannot be reconciled. We, five independent groups with a longstanding interest in the molecular biology of...

BackgroundMutations in the KIAA2022 gene have been reported in male patients with X-linked intellectual disability, and related female carriers were unaffected. Here, we report 14 female patients who carry a heterozygous de novo KIAA2022 mutation and share a phenotype characterised by intellectual disability and epilepsy.MethodsReported females were selected for genetic testing because of substantial developmental problems and/or epilepsy. X-inactivation and expression studies were performed when possible.ResultsAll mutations were predicted to result in a frameshift or premature stop. 12 out of 14 patients had intractable epilepsy with myoclonic and/or absence seizures, and generalised in 11. Thirteen patients had mild to severe intellectual disability. This female phenotype partially overlaps with the reported male phenotype which consists of more severe intellectual disability, microcephaly, growth retardation, facial dysmorphisms and, less frequently, epilepsy. One female patient showed completely skewed X-inactivation, complete absence of RNA expression in blood and a phenotype similar to male patients. In the six other tested patients, X-inactivation was random, confirmed by a non-significant twofold to threefold decrease of RNA expression in blood, consistent with the expected mosaicism between cells expressing mutant or normal KIAA2022 alleles.ConclusionsHeterozygous loss of KIAA2022 expression is a cause of intellectual disability in females. Compared with its hemizygous male counterpart, the heterozygous female disease has less severe intellectual disability, but is more often associated with a severe and intractable myoclonic epilepsy.

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