Search

Ataxin-2 (ATXN2) is a gene implicated in spinocerebellar ataxia type II (SCA2), amyotrophic lateral sclerosis (ALS) and Parkinsonism. The encoded protein is a therapeutic target for ALS and related conditions. ATXN2 (or Atx2 in insects) can function in translational activation, translational repression, mRNA stability and in the assembly of mRNP-granules, a process mediated by intrinsically disordered regions (IDRs). Previous work has shown that the LSm (Like-Sm) domain of Atx2, which can help stimulate mRNA translation, antagonizes mRNP-granule assembly. Here we advance these findings through a series of experiments on Drosophila and human Ataxin-2 proteins. Results of Targets of RNA Binding Proteins Identified by Editing (TRIBE), co-localization and immunoprecipitation experiments indicate that a polyA-binding protein (PABP) interacting, PAM2 motif of Ataxin-2 may be a major determinant of the mRNA and protein content of Ataxin-2 mRNP granules. Transgenic Experiments with transgenic Drosophila indicate that while the Atx2-LSm domain may protect against neurodegeneration, structured PAM2- and unstructured IDR- interactions both support Atx2-induced cytotoxicity. Taken together, the data lead to a proposal for how Ataxin-2 interactions are remodelled during translational control and how structured and non-structured interactions contribute differently to the specificity and efficiency of RNP granule condensation as well as to neurodegeneration. Author summary: Mutations in genes that promote protein aggregation are primarily associated with neurodegenerative diseases. RNA-binding proteins, crucial for gene regulation and cellular stress response, are also major constituents of protein aggregate-rich mRNP granules. Recent studies aim to understand the molecular mechanisms governing the formation of stress granules identified Intrinsically Disordered Regions (IDRs) within mRNP granule proteins as a key factor that facilitates the formation of amyloid-like structures. A deeper understanding of stress granule dynamics holds promise for elucidating neurodegenerative disease mechanisms. Ataxin-2, is an RNA-binding protein implicated in neurodegenerative disorders like spinocerebellar ataxia type II, amyotrophic lateral sclerosis, and Parkinsonism. Reducing the levels of Ataxin-2 levels or deleting its IDR prevents RNP aggregation and offers neuroprotection in animal models of neurodegenerative diseases. We show that deleting the structured LSm domain of Ataxin-2, which impedes granule assembly, enhances cytotoxicity. Moreover, specific molecular interactions involving Ataxin-2 PAM2 motif binding to polyA-binding protein is crucial for recruiting mRNAs and other proteins into RNP granules. These interactions not only shape granule composition but also influence disease progression. Our findings propose a model illustrating the dynamic remodeling of Ataxin-2 interactions, emphasizing the distinct roles of structured and unstructured domains in governing mRNP-granule condensation and neurodegeneration. [ABSTRACT FROM AUTHOR]

Most mutations that truncate the reading frame of the DMD gene cause loss of dystrophin expression and lead to Duchenne muscular dystrophy. However, amelioration of disease severity has been shown to result from alternative translation initiation beginning in DMD exon 6 that leads to expression of a highly functional N-truncated dystrophin. Here we demonstrate that this isoform results from usage of an internal ribosome entry site (IRES) within exon 5 that is glucocorticoid inducible. We confirmed IRES activity by both peptide sequencing and ribosome profiling in muscle from individuals with minimal symptoms despite the presence of truncating mutations. We generated a truncated reading frame upstream of the IRES by exon skipping, which led to synthesis of a functional N-truncated isoform in both human subject-derived cell lines and in a new DMD mouse model, where expression of the truncated isoform protected muscle from contraction-induced injury and corrected muscle force to the same level as that observed in control mice. These results support a potential therapeutic approach for patients with mutations within the 5' exons of DMD., Mutations in the DMD gene result in either the more severe Duchenne muscular dystrophy (DMD) or the milder Becker muscular dystrophy (BMD). The phenotype generally depends on whether the mutation [...]

In the version of this article initially published online, the nucleotide numbering of the AS (-3 to + 16), B (+17 to +40) and C (+49 to -10) targeted sequences [...]

A null mutation of the Drosophila calcium/calmodulin-dependent protein kinase II gene (CaMKII) was generated using homologous recombination. Null animals survive to larval and pupal stages due to a large maternal contribution of CaMKII mRNA, which consists of a short 3'-untranslated region (UTR) form lacking regulatory elements that guide local translation. The selective loss of the long 3'UTR mRNA in CaMKII-null larvae allows us to test its role in plasticity. Development and evoked function of the larval neuromuscular junction are surprisingly normal, but the resting rate of miniature excitatory junctional potentials (mEJPs) is significantly lower in CaMKII mutants. Mutants also lack the ability to increase mEJP rate in response to spaced depolarization, a type of activity-dependent plasticity shown to require both transcription and translation. Consistent with this, overexpression of miR-289 in wild-type animals blocks plasticity of spontaneous release. In addition to the defects in regulation of mEJP rate, CaMKII protein is largely lost from synapses in the mutant. All phenotypes are non-sex-specific and rescued by a fosmid containing the entire wild-type CaMKII locus, but only viability and CaMKII localization are rescued by genomic fosmids lacking the long 3'UTR. This suggests that synaptic CaMKII accumulates by two distinct mechanisms: local synthesis requiring the long 3'UTR form of CaMKII mRNA and a process that requires zygotic transcription of CaMKII mRNA. The origin of synaptic CaMKII also dictates its functionality. Locally translated CaMKII has a privileged role in regulation of spontaneous release, which cannot be fulfilled by synaptic CaMKII from the other pool. [ABSTRACT FROM AUTHOR]

In the version ofthis article initially published online, the nucleotide numbering of the AS (-3 to + 16), B (+17 to +40) and C (+49 to -10) targeted sequences in [...]

The Ataxin-2 (Atx2) protein contributes to the progression of neurodegenerative phenotypes in animal models of amyotrophic lateral sclerosis (ALS), type 2 spinocerebellar ataxia (SCA-2), Parkinson's disease, and Huntington's disease (HD). However, because the Atx2 protein contains multiple separable activities, deeper understanding requires experiments to address the exact mechanisms by which Atx2 modulates neurodegeneration (ND) progression. Recent work on two ALS models, C9ORF72 and FUS, in Drosophila has shown that a C-terminal intrinsically disordered region (cIDR) of Atx2 protein, required for assembly of ribonucleoprotein (RNP) granules, is essential for the progression of neurodegenerative phenotypes as well as for accumulation of protein inclusions associated with these ALS models. Here, we show that the Atx2-cIDR also similarly contributes to the progression of degenerative phenotypes and accumulation of Huntingtin protein aggregates in Drosophila models of HD. Because Huntingtin is not an established component of RNP granules, these observations support a recently hypothesized, unexpected protein-handling function for RNP granules, which could contribute to the progression of Huntington's disease and, potentially, other proteinopathies., (© The Author(s) 2021. Published by Oxford University Press on behalf of Genetics Society of America.)

mRNA polyadenylation functions in nuclear export, translation, and stability. We describe an efficient protocol designed to assess poly(A) tail length that is based on 3' tailing by yeast poly(A) polymerase and product analysis to single-nucleotide resolution by capillary electrophoresis.