Elongator mutation in mice induces neurodegeneration and ataxia-like behavior

Cerebellar ataxias are severe neurodegenerative disorders with an early onset and progressive and inexorable course of the disease. Here, we report a single point mutation in the gene encoding Elongator complex subunit 6 causing Purkinje neuron degeneration and an ataxia-like phenotype in the mutant wobbly mouse. This mutation destabilizes the complex and compromises its function in translation regulation, leading to protein misfolding, proteotoxic stress, and eventual neuronal death. In addition, we show that substantial microgliosis is triggered by the NLRP3 inflammasome pathway in the cerebellum and that blocking NLRP3 function in vivo significantly delays neuronal degeneration and the onset of ataxia in mutant animals. Our data provide a mechanistic insight into the pathophysiology of a cerebellar ataxia caused by an Elongator mutation, substantiating the increasing body of evidence that alterations of this complex are broadly implicated in the onset of a number of diverse neurological disorders.The authors acknowledge the facilities, and the scientific and technical assistance of the Australian Phenomics Facility (APF), the Australian National University. The APF is supported by the Australian Phenomics Network (APN). The APN is supported by the Australian Government through the National Collaborative Research Infrastructure Strategy (NCRIS) program. We are very grateful to Jelena Bezbradica Mirkovic and Kate Schroder for providing NLRP3 KO and Caspase-1 KO animals and for their valuable discussion. We also thank Avril Robertson and Matthew Cooper for the gift of MCC950 and Trent Woodruff for advice regarding the administration of MCC950. We acknowledge Ting-Yu Lin and Andrzej Chramiec-Głąbik for providing labeled tRNAs. This work was supported by the POLONEZ1 Grant UMO-2015/19/P/NZ1/02514 from the National Science Centre, Poland and received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 665778 (M.G. and A.S.-K.) and the First Team grant First TEAM/ 2016-1/2 from the Foundation for Polish Science (S.G.)

Molecular insights into RNA recognition and gene regulation by the TRIM-NHL protein Mei-P26

The TRIM-NHL protein Meiotic P26 (Mei-P26) acts as a regulator of cell fate in Drosophila. Its activity is critical for ovarian germline stem cell maintenance, differentiation of oocytes, and spermatogenesis. Mei-P26 functions as a post-transcriptional regulator of gene expression; however, the molecular details of how its NHL domain selectively recognizes and regulates its mRNA targets have remained elusive. Here, we present the crystal structure of the Mei-P26 NHL domain at 1.6 Å resolution and identify key amino acids that confer substrate specificity and distinguish Mei-P26 from closely related TRIM-NHL proteins. Furthermore, we identify mRNA targets of Mei-P26 in cultured Drosophila cells and show that Mei-P26 can act as either a repressor or activator of gene expression on different RNA targets. Our work reveals the molecular basis of RNA recognition by Mei-P26 and the fundamental functional differences between otherwise very similar TRIM-NHL proteins

The role of the metabotropic glutamate receptors mGluR5 and dopamine receptors D2 in the development of cognitive deficits in the ketamine model of schizophrenia

Schizofrenia jest poważną chorobą psychiczną dotykającą około 1% populacji ludzkiej. Pomimo wielu badań prowadzonych na całym świecie, etiopatogeneza tej choroby nie została dotychczas w pełni wyjaśniona. W kontekście rozwoju wiedzy dotyczącej tego schorzenia niezmiernie ważne jest znalezienie modelu zwierzęcego, w którym możliwe jest wytworzenie wszystkich objawów schizofrenii, tj. objawów wytwórczych, takich jak halucynacje, omamy i urojenia oraz ubytkowych, do których zalicza się: otępienie, apatię, anhedonię, depresję i zaburzenia procesów poznawczych. Obiecującą odpowiedzią na tę potrzebę jest model zwierzęcy oparty na inhibicji transmisji glutaminianergicznej przez receptory NMDA za pomocą ich niekompetycyjnego antagonisty - ketaminy.W niniejszej pracy postanowiono wykorzystać ten model w celu dokładniejszego poznania mechanizmów związanych z występowaniem zaburzeń poznawczych. Zastosowano dwa odrębne podejścia: aby potwierdzić wystąpienie deficytów pamięci przestrzennej u zwierząt po chronicznym podaniu ketaminy zastosowano behawioralny test rozpoznawania nowego obiektu, natomiast w celu zbadania ewentualnych zmian w mózgu użyto hybrydyzacji in situ oraz autoradiografii wiązania radioliganda do receptora na skrawkach mózgów szczurzych. Ze względu na dwie farmakologiczne teorie schizofrenii - glutaminianergiczną i dopaminergiczną, zdecydowano się sprawdzić rolę receptorów metabotropowych dla glutaminianu mGluR5 oraz dopaminowych D2 w powstawaniu deficytów pamięci przestrzennej.Przeprowadzone badania behawioralne potwierdziły występowanie deficytów pamięci przestrzennej u zwierząt w ketaminowym modelu schizofrenii, które są efektem inhibicji procesów plastyczności synaptycznej zależnych od receptora NMDA. Ponadto wykonane analizy biochemiczne wykazały wzrost poziomu mRNA oraz białka dla receptora mGluR5 w regionie CA1 i CA3 części grzbietowej hipokampa. Zaobserwowana zmiana najprawdopodobniej stanowi mechanizm adaptacyjny, przeciwdziałający deficytom pamięci przestrzennej, powstałym po zablokowaniu receptorów NMDA. Badania dotyczące receptora dopaminowego D2 nie wykazały istotnie statystycznych różnic w poziomie mRNA i białka receptora D2 pomiędzy grupą kontrolną, a zwierzętami po chronicznym podaniu ketaminy dla żadnej z badanych struktur mózgu. Na tej podstawie wnioskowano, że psychozy wywołane podaniem ketaminy nie zaburzają trwale transmisji dopaminergicznej.Na podstawie uzyskanych wyników stwierdzono, że mechanizmem powstawania deficytów pamięci przestrzennej u zwierząt w ketaminowym modelu schizofrenii są zaburzenia w transmisji glutaminianericznej przez receptory NMDA, a receptory mGluR5 są istotne, jako białka biorące udział w przeciwdziałaniu efektom wytworzonych deficytów poznawczych.Schizophrenia is serious psychiatric disorder, which affects approximately 1% of the population. Despite of a huge number of experiments, the molecular mechanisms of the disease are still poorly understood. In context of studies concerning this disorder it is at utmost importance to address the matter of finding a suitable animal model, in which all the symptoms of schizophrenia i.e. positive symptoms such as hallucinations, delusions and negative symptoms composed of numbness, apathy, anhedonia, depression and cognitive deficits could be replicated. An animal model based on inhibition of glutamatergic transmission by blocking NMDA receptors using a non-competitive antagonist - ketamine.In the present studies, it has been decided to use this model as a tool for better understanding of mechanisms concerning occurrences of cognitive deficits. Two approaches have been used: to confirm induction of spatial memory deficits in animals after repeated doses of ketamine the behavioral Novel Object Recognition Test has been used, and to examine possible biochemical alterations in the brain - in situ hybridization and quantitative autoradiography in the brain slices. With regard to pharmacological theories of schizophrenia: glutamatergic and dopaminergic - the role of metabotropic glutamatergic receptors - mGluR5 and dopaminergic D2 in the formation of spatial memory deficits has been studied.Behavioral test confirmed spatial memory deficits in animals induced by repeated dosing of ketamine, which are caused by inhibition of NMDA - dependent synaptic plasticity. Furthermore, biochemical analysis showed increased levels of mRNA and protein for mGluR5 receptor in regions CA1 and CA3 of the dorsal hippocampus, what the most probably might be regarded as an adaptive response counteracting spatial memory deficits caused by blocking of the NMDA channels. Experiments concerning dopamine D2 receptor did not indicate any statistically relevant differences between the levels of mRNA and protein of the D2 receptor between the control group and animals treated repeatedly with ketamine in none of the examined brain regions. On this basis it has been concluded, that psychosis caused by ketamine administration does not permanently disturb dopaminergic transmission.Based on the obtained results it has been concluded, that spatial memory deficits in animals in ketamine model of schizophrenia are caused by disturbances in glutamatergic transmission via NMDA receptor, and mGluR5 are relevant as proteins taking part in countering the effects of produced cognitive deficits

Dual agonistic and antagonistic roles of ZC3H18 provide for co-activation of distinct nuclear RNA decay pathways

Summary: The RNA exosome is a versatile ribonuclease. In the nucleoplasm of mammalian cells, it is assisted by its adaptors the nuclear exosome targeting (NEXT) complex and the poly(A) exosome targeting (PAXT) connection. Via its association with the ARS2 and ZC3H18 proteins, NEXT/exosome is recruited to capped and short unadenylated transcripts. Conversely, PAXT/exosome is considered to target longer and adenylated substrates via their poly(A) tails. Here, mutational analysis of the core PAXT component ZFC3H1 uncovers a separate branch of the PAXT pathway, which targets short adenylated RNAs and relies on a direct ARS2-ZFC3H1 interaction. We further demonstrate that similar acidic-rich short linear motifs of ZFC3H1 and ZC3H18 compete for a common ARS2 epitope. Consequently, while promoting NEXT function, ZC3H18 antagonizes PAXT activity. We suggest that this organization of RNA decay complexes provides co-activation of NEXT and PAXT at loci with abundant production of short exosome substrates

Elongator mutation in mice induces neurodegeneration and ataxia-like behavior

Cerebellar ataxias are severe neurodegenerative disorders with an early onset and progressive and inexorable course of the disease. Here, we report a single point mutation in the gene encoding Elongator complex subunit 6 causing Purkinje neuron degeneration and an ataxia-like phenotype in the mutant wobbly mouse. This mutation destabilizes the complex and compromises its function in translation regulation, leading to protein misfolding, proteotoxic stress, and eventual neuronal death. In addition, we show that substantial microgliosis is triggered by the NLRP3 inflammasome pathway in the cerebellum and that blocking NLRP3 function in vivo significantly delays neuronal degeneration and the onset of ataxia in mutant animals. Our data provide a mechanistic insight into the pathophysiology of a cerebellar ataxia caused by an Elongator mutation, substantiating the increasing body of evidence that alterations of this complex are broadly implicated in the onset of a number of diverse neurological disorders

Elp2 mutations perturb the epitranscriptome and lead to a complex neurodevelopmental phenotype

Intellectual disability (ID) and autism spectrum disorder (ASD) are the most common neurodevelopmental disorders and are characterized by substantial impairment in intellectual and adaptive functioning, with their genetic and molecular basis remaining largely unknown. Here, we identify biallelic variants in the gene encoding one of the Elongator complex subunits, ELP2, in patients with ID and ASD. Modelling the variants in mice recapitulates the patient features, with brain imaging and tractography analysis revealing microcephaly, loss of white matter tract integrity and an aberrant functional connectome. We show that the Elp2 mutations negatively impact the activity of the complex and its function in translation via tRNA modification. Further, we elucidate that the mutations perturb protein homeostasis leading to impaired neurogenesis, myelin loss and neurodegeneration. Collectively, our data demonstrate an unexpected role for tRNA modification in the pathogenesis of monogenic ID and ASD and define Elp2 as a key regulator of brain development.</p