Neurotransmission defects and motoneuron degeneration are hallmarks of spinal muscular atrophy, a monogenetic disease caused by the deficiency of the SMN protein. In the present study, we show that systemic application of R-Roscovitine, a Ca v 2.1/Ca v 2.2 channel modifier and a cyclin-dependent kinase 5 (Cdk-5) inhibitor, significantly improved survival of SMA mice. In addition, R-Roscovitine increased Ca v 2.1 channel density and sizes of the motor endplates. In vitro, R-Roscovitine restored axon lengths and growth cone sizes of Smn-deficient motoneurons corresponding to enhanced spontaneous Ca 2+ influx and elevated Ca v 2.2 channel cluster formations independent of its capability to inhibit Cdk-5. Acute application of R-Roscovitine at the neuromuscular junction significantly increased evoked neurotransmitter release, increased the frequency of spontaneous miniature potentials, and lowered the activation threshold of silent terminals. These data indicate that R-Roscovitine improves Ca 2+ signaling and Ca 2+ homeostasis in Smn-deficient motoneurons, which is generally crucial for motoneuron differentiation, maturation, and function.

Gene expression requires tight coordination of the molecular machineries that mediate transcription and splicing. While the interplay between transcription kinetics and spliceosome fidelity has been investigated before, less is known about mechanisms regulating the assembly of the spliceosomal machinery in response to transcription changes. Here, we report an association of the Smn complex, which mediates spliceosomal snRNP biogenesis, with the 7SK complex involved in transcriptional regulation. We found that Smn interacts with the 7SK core components Larp7 and Mepce and specifically associates with 7SK subcomplexes containing hnRNP R. The association between Smn and 7SK complexes is enhanced upon transcriptional inhibition leading to reduced production of snRNPs. Taken together, our findings reveal a functional association of Smn and 7SK complexes that is governed by global changes in transcription. Thus, in addition to its canonical nuclear role in transcriptional regulation, 7SK has cytosolic functions in fine-tuning spliceosome production according to transcriptional demand.

Background Major efforts have been made in the last decade to develop and improve therapies for proximal spinal muscular atrophy (SMA). The introduction of Nusinersen/Spinraza™ as an antisense oligonucleotide therapy, Onasemnogene abeparvovec/Zolgensma™ as an AAV9-based gene therapy and Risdiplam/Evrysdi™ as a small molecule modifier of pre-mRNA splicing have set new standards for interference with neurodegeneration. Main body Therapies for SMA are designed to interfere with the cellular basis of the disease by modifying pre-mRNA splicing and enhancing expression of the Survival Motor Neuron (SMN) protein, which is only expressed at low levels in this disorder. The corresponding strategies also can be applied to other disease mechanisms caused by loss of function or toxic gain of function mutations. The development of therapies for SMA was based on the use of cell culture systems and mouse models, as well as innovative clinical trials that included readouts that had originally been introduced and optimized in preclinical studies. This is summarized in the first part of this review. The second part discusses current developments and perspectives for amyotrophic lateral sclerosis, muscular dystrophies, Parkinson's and Alzheimer's disease, as well as the obstacles that need to be overcome to introduce RNA-based therapies and gene therapies for these disorders. Conclusion RNA-based therapies offer chances for therapy development of complex neurodegenerative disorders such as amyotrophic lateral sclerosis, muscular dystrophies, Parkinson’s and Alzheimer’s disease. The experiences made with these new drugs for SMA, and also the experiences in AAV gene therapies could help to broaden the spectrum of current approaches to interfere with pathophysiological mechanisms in neurodegeneration.

Neurons critically rely on the functions of RNA-binding proteins to maintain their polarity and resistance to neurotoxic stress. HnRNP R has a diverse range of post-transcriptional regulatory functions and is important for neuronal development by regulating axon growth. Hnrnpr pre-mRNA undergoes alternative splicing giving rise to a full-length protein and a shorter isoform lacking its N-terminal acidic domain. To investigate functions selectively associated with the full-length hnRNP R isoform, we generated a Hnrnpr knockout mouse (Hnrnprtm1a/tm1a) in which expression of full-length hnRNP R was abolished while production of the truncated hnRNP R isoform was retained. Motoneurons cultured from Hnrnprtm1a/tm1a mice did not show any axonal growth defects but exhibited enhanced accumulation of double-strand breaks and an impaired DNA damage response upon exposure to genotoxic agents. Proteomic analysis of the hnRNP R interactome revealed the multifunctional protein Yb1 as a top interactor. Yb1-depleted motoneurons were defective in DNA damage repair. We show that Yb1 is recruited to chromatin upon DNA damage where it interacts with γ-H2AX, a mechanism that is dependent on full-length hnRNP R. Our findings thus suggest a novel role of hnRNP R in maintaining genomic integrity and highlight the function of its N-terminal acidic domain in this context.

In neurons, endoplasmic reticulum forms a highly dynamic network that enters axons and presynaptic terminals and plays a central role in Ca2+ homeostasis and synapse maintenance. However, the underlying mechanisms involved in regulation of its dynamic remodeling as well as its function in axon development and presynaptic differentiation remain elusive. Here, we used high resolution microscopy and live cell imaging to investigate rapid movements of endoplasmic reticulum and ribosomes in axons of cultured motoneurons after stimulation with Brain-derived neurotrophic factor. Our results indicate that the endoplasmic reticulum extends into axonal growth cone filopodia where its integrity and dynamic remodeling are regulated mainly by actin and its motor protein myosin VI. Additionally, we found that in axonal growth cones, ribosomes assemble into 80S subunits within seconds and associate with ER in response to extracellular stimuli which describes a novel function of axonal ER in dynamic regulation of local translation.