Project Details
Projekt
Axonal mRNP alterations in spinal muscular atrophy
Applicants
Dr. Michael Briese; Professor Dr. Michael A. Sendtner
Subject Area
General Genetics and Functional Genome Biology
Term
from 2016 to 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 313233411
Spinal motoneurons are highly polarized cells that critically depend on subcellular mRNA transport into axons during development and for maintenance and repair in the adult. Axonal mRNA transport is disturbed in motoneuron diseases and might contribute to defective axon integrity and synaptic transmission at neuromuscular endplates, thereby causing motoneuron dysfunction and death. Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder characterized by loss of motoneurons in the spinal cord leading to weakness of corresponding muscles. Patients have a deletion of or mutations in the Survival Motor Neuron 1 (SMN1) gene leading to loss of the SMN protein. SMN has a canonical function in the biogenesis of spliceosomal snRNPs. More recent research has pointed to additional functions in the assembly and transport of messenger ribonucleoprotein particles (mRNPs). Disturbed mRNP transport and processing might contribute to motor axon degeneration and defective presynaptic differentiation seen in SMA. We have previously identified the heterogeneous nuclear ribonucleoprotein R (hnRNP R), an RNA-binding protein, as an interactor of SMN. Reduction of either Smn or hnRNP R in cultured primary mouse motoneurons leads to reduced axon growth indicating that both proteins have roles in motoneuron development. Levels of hnRNP R are severely reduced in axons of Smn-deficient motoneurons indicating reduced transport or processing of axonal hnRNP R and hnRNP R-containing mRNPs upon loss of Smn. During the first SPP 1935 funding period we further explored this possibility by characterizing the RNA interactome of hnRNP R using the iCLIP technique and observed interactions with many mRNAs encoding proteins with functions in axon growth. Additionally, we characterized the protein interactome of hnRNP R in motoneurons by proteomics and detected a large number of RNA-binding proteins, including several proteins previously implicated in amyotrophic lateral sclerosis (ALS). Beyond that, we found that the Hnrnpr transcript itself is transported into motor axons. We identified proteins interacting with the 3'UTR that might mediate its axonal translocation. During the second SPP 1935 funding period we would like to characterize the hnRNP R transport mRNPs in vivo and investigate to what extent their integrity is disturbed in motor nerves from an SMA mouse model. Additionally, we would like to examine whether transport and local translation of Hnrnpr is disrupted in Smn-deficient motoneurons and in motor nerves from SMA mice. Finally, we are planning to investigate the functions of hnRNP R for motor system development and maintenance by characterizing a new Hnrnpr knockout mouse. We anticipate that our findings are not only relevant for SMA but might also reveal new insights into the pathomechanisms of ALS, and envision that our expertise in motoneuron biology is of interest to other members of the SPP 1935.
DFG Programme
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