Gle1 is required for tRNA to stimulate Dbp5 ATPase activity in vitro and to promote Dbp5 mediated tRNA export in vivo

Cells must maintain a pool of processed and charged transfer RNAs (tRNA) to sustain translation capacity and efficiency. Numerous parallel pathways support the processing and directional movement of tRNA in and out of the nucleus to meet this cellular demand. Recently, several proteins known to control messenger RNA (mRNA) transport were implicated in tRNA export. The DEAD-box Protein 5, Dbp5, is one such example. In this study, genetic and molecular evidence demonstrates that Dbp5 functions parallel to the canonical tRNA export factor Los1. In vivo co-immunoprecipitation data further shows Dbp5 is recruited to tRNA independent of Los1, Msn5 (another tRNA export factor), or Mex67 (mRNA export adaptor), which contrasts with Dbp5 recruitment to mRNA that is abolished upon loss of Mex67 function. However, as with mRNA export, overexpression of Dbp5 dominant-negative mutants indicates a functional ATPase cycle and that binding of Dbp5 to Gle1 is required by Dbp5 to direct tRNA export. Biochemical characterization of the Dbp5 catalytic cycle demonstrates the direct interaction of Dbp5 with tRNA (or double stranded RNA) does not activate Dbp5 ATPase activity, rather tRNA acts synergistically with Gle1 to fully activate Dbp5. These data suggest a model where Dbp5 directly binds tRNA to mediate export, which is spatially regulated via Dbp5 ATPase activation at nuclear pore complexes by Gle1.

Identification of novel nuclear pore complex associated proteins in esophageal carcinoma by an integrated bioinformatics analysis

Nucleoporins (NUPs) are components of the nuclear pore complex (NPC) that participate in the nucleocytoplasmic transport of macromolecules as well as in many essential processes that may be led to carcinogenesis. We selected three expression profile microarray datasets from GEO and as well as TCGA data to identify differentially expressed NUPs genes in esophageal carcinoma. Our findings indicated that NUP133, NUP37, NUP43, NUP50, GLE1 and NDC1 are overexpressed in esophageal carcinoma, among which NUP50 and GLE1genes are reported for the first time in esophageal carcinoma. All identified NUPs were also associated with distant metastasis.Communicated by Ramaswamy H. Sarma.

Mutation Screening of the GLE1 Gene in a Large Chinese Cohort of Amyotrophic Lateral Sclerosis Patients

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disease involving the upper and lower motor neurons of the spinal cord, brainstem, and cerebral cortex. At least 30 genes have been implicated in familial ALS (fALS) and sporadic ALS (sALS). Kaneb et al. (2015) first carried out a large-scale sequencing study in ALS patients and identified two loss-of-function (LOF) variants in the GLE1 gene. The LOF mutation-induced disruption of RNA metabolism through the haploinsufficiency mechanism is implicated in ALS pathogenesis. A total of 628 ALS patients and 522 individuals without neurodegenerative disorders were enrolled in this study to explore the GLE1 gene contribution to ALS in the Chinese population. All 16 exons and the flanking intron of GLE1 were screened by Sanger sequencing. In total, we identified seven rare GLE1 coding variants, including one novel nonsense mutation and six rare missense mutations in 628 ALS patients. The frequency of GLE1 LOF mutations was 0.16% (1/628) among Chinese sALS patients, implying that it is an uncommon genetic determinant of ALS in Chinese patients. Additionally, the rare missense variants in the hCG1-binding domain of GLE1 impairing the distribution of the hGle1B isoform at the nuclear pore complex (NPC) region may be involved in the pathogenesis of ALS.

Emerging molecular functions and novel roles for the DEAD-box protein Dbp5/DDX19 in gene expression

The DEAD-box protein (DBP) Dbp5, a member of the superfamily II (SFII) helicases, has multiple reported roles in gene expression. First identified as an essential regulator of mRNA export in Saccharomyces cerevisiae, the enzyme now has reported functions in non-coding RNA export, translation, transcription, and DNA metabolism. Localization of the protein to various cellular compartments (nucleoplasm, nuclear envelope, and cytoplasm) highlights the ability of Dbp5 to modulate different stages of the RNA lifecycle. While Dbp5 has been well studied for > 20 years, several critical questions remain regarding the mechanistic principles that govern Dbp5 localization, substrate selection, and functions in gene expression. This review aims to take a holistic view of the proposed functions of Dbp5 and evaluate models that accommodate current published data.

Extension of the phenotypic spectrum of GLE1-related disorders to a mild congenital form resembling congenital myopathy

Background

GLE1 (GLE1, RNA Export Mediator, OMIM#603371) variants are associated with severe autosomal recessive motor neuron diseases, that are lethal congenital contracture syndrome 1 (LCCS1, OMIM#253310) and congenital arthrogryposis with anterior horn cell disease (CAAHD, OMIM#611890).

The clinical spectrum of GLE1‐related disorders has been expanding these past years, including with adult‐onset amyotrophic lateral sclerosis (ALS) GLE1‐related forms, especially through the new molecular diagnosis strategies associated with the emergence of next‐generation sequencing (NGS) technologies. However, despite this phenotypic variability, reported congenital or ALS adult‐onset forms remain severe, leading to premature death.

Methods

Through multidisciplinary interactions between our Neuropediatric and Medical Genetics departments, we were able to diagnose two siblings presenting with congenital disorder, using an NGS approach accordingly to the novel French national recommendations.

Results

Two siblings with very similar clinical features, meaning neuromuscular disorder of neonatal onset with progressive improvement, were examined in our Neuropediatrics department. The clinical presentation evoked initially congenital myopathy with autosomal recessive inheritance. However, additional symptoms such as mild dysmorphic features including high anterior hairline, downslanted palpebral fissures, anteverted nares, smooth philtrum with thin upper‐lip, narrow mouth and microretrognathia or delayed expressive language and postnatal growth retardation were suggestive of a more complex clinical presentation and molecular diagnosis. Our NGS approach revealed an unexpected molecular diagnosis for these two siblings, meaning the presence of the homozygous c.1808G>T GLE1 variant.

Conclusions

We here report the mildest phenotype ever described, in two siblings carrying the homozygous c.1808G>T GLE1 variant, further widening the clinical spectrum of GLE1‐related diseases. Moreover, by reflecting current medical practice, this case report confirms the importance of establishing regular multidisciplinary meetings, essential for discussing such difficult clinical presentations to finally enable molecular diagnosis, especially when NGS technologies are used.

The expression of SMN1, MART3, GLE1 and FUS genes in spinal muscular atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) is one of the most common genetic causes of death in infants due to a mutation of the motor neuron 1 (SMN1) gene. The SMN1 gene encodes for the multifunctional SMN protein. SMN has been shown to be implicated in pre-mRNA splicing, mRNA transport and translational control. Also other mRNA processing proteins, such as GLE1, Marten (MART3) and Fused in Sarcoma (FUS), have been linked to neurodegenerative diseases. The aim of the study was to determine the expression of SMN, GLE1, MART3 and FUS genes in cell lines of the fibroblasts derived from SMA patients and normal controls.

MATERIAL AND METHODS

Total RNA was extracted from purchased fibroblasts acquired from three SMA type I patients and fibroblasts of three age-matched healthy controls. The RNA was then subjected to qPCR analysis using primers specific for the GLE1, MART3, FUS and SMN1 genes vs. GAPDH as internal control gene.

RESULTS

SMN1 mRNA levels were at least ×10 lower in fibroblasts of SMA patients compared to controls. Gle1 and MART3 gene expression was ×2 downregulated whereas FUS mRNA levels appeared to be ×3 upregulated in SMA cells when compared to controls. We found a high correlation between FUS gene expression level to the SMN1 at gene expression level of fibroblast cell lines of SMA type I patients (r = 0.994, p < 0.0001).

CONCLUSIONS

Our preliminary data show an intriguing expression profile of Gle1, MART3 and FUS genes in SMA, and suggest a critical role of FUS protein in the SMA pathogenesis.

Identification of the Novel Nup188-brr7 Allele in a Screen for Cold-Sensitive mRNA Export Mutants in Saccharomyces cerevisiae

The maturation and export of mRNA from the nucleus through the nuclear pore complex is critical for maintaining an appropriate proteome in all eukaryotic cells. Here we summarize a previously unpublished screen in S. cerevisiae that utilized an established dT50 in situ hybridization assay to identify cold-sensitive mutants that accumulated bulk poly A RNA in the nucleus. The screen identified seven mutants in six complementation groups, including the brr6-1 strain that we described previously. In addition to brr6-1, we identified novel alleles of the key transport gene GLE1 and NUP188, a component of the Nic96 nucleoporin complex. Notably, we show that the nup188-brr7 allele causes defects in select protein import pathways as well as mRNA export. Given recent structural and functional evidence linking the Nic96 complex to transport components, this mutant may be particularly useful to the transport community.

Screening of GLE1 mutations in Chinese amyotrophic lateral sclerosis patients

Amyotrophic lateral sclerosis (ALS) is a lethal neurological disease primarily involving the spinal cord, brainstem, and corticospinal tract. Recently, mutations in the GLE1 gene were reported in Caucasian ALS patients. To inquire whether Chinese ALS patients carried causal mutations in the gene, we screened all 16 coding exons of GLE1 with Sanger sequencing in a Han Chinese cohort of 250 ALS cases. No nonsynonymous coding variants were detected. Our results suggest that pathogenic variants in the GLE1 gene are rare in Chinese ALS patients.

A homozygous I684T in GLE1 as a novel cause of arthrogryposis and motor neuron loss

Mutations in GLE1, RNA export mediator (GLE1) gene have previously been shown to cause motor neuron diseases such as lethal congenital contracture syndrome 1 (LCCS1) and lethal arthrogryposis with anterior horn cell disease (LAAHD), including arthrogryposis, fetal akinesis and motor neuron loss as common clinical features. The homozygous Fin_Major mutation p.T144_E145insPFQ has been described as one of the causes for LCCS1 whereas LAAHD is caused by a heterocompound Fin_Major mutation together with p.R569H, p.V617M or p.I684T missense mutation. None of these heterocompound missense mutations have previously been reported as homozygous states. Here we present the clinical features of 2 siblings with a homozygous p.I684T mutation in GLE1. The patients suffered from similar, but milder symptoms than in LCCS1 and LAAHD, surviving up to 6 months before they died due to a progressive disease course including respiratory failure. Arthrogryposis, lack of spontaneous movements, and epilepsy were notable in both cases and lack of anterior horn cells was identified in autopsy samples. Our studies on patient-derived fibroblasts show that the homozygous p.I684T impairs the nuclear localization of GLE1 further confirming the pathogenic role of this mutation.

Survival beyond the perinatal period expands the phenotypes caused by mutations in GLE1

Mutations in GLE1 underlie Lethal Congenital Contracture syndrome (LCCS) and Lethal Arthrogryposis with Anterior Horn Cell Disease (LAAHD). Both LCCS and LAAHD are characterized by reduced fetal movements, congenital contractures, and a severe form of motor neuron disease that results in fetal death or death in the perinatal period, respectively. We identified bi-allelic mutations in GLE1 in two unrelated individuals with motor delays, feeding difficulties, and respiratory insufficiency who survived beyond the perinatal period. Each affected child had missense variants predicted to result in amino acid substitutions near the C-terminus of GLE1 that are predicted to disrupt protein-protein interaction or GLE1 protein targeting. We hypothesize that mutations that preserve function of the coiled-coil domain of GLE1 cause LAAHD whereas mutations that abolish the function of the coiled-coil domain cause LCCS. The phenotype of LAAHD is now expanded to include multiple individuals surviving into childhood suggesting that LAAHD is a misnomer and should be re-named Arthrogryposis with Anterior Horn Cell Disease (AAHD).