The ALS disease protein TDP-43 is actively transported in motor neuron axons and regulates axon outgrowth.
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease specifically affecting cortical and spinal motor neurons. Cytoplasmic inclusions containing hyperphosphorylated and ubiquitinated TDP-43 are a pathological hallmark of ALS, and mutations in the gene encoding TDP-43 have been directly linked to the development of the disease. TDP-43 is a ubiquitous DNA/RNA-binding protein with a nuclear role in pre-mRNA splicing. However, the selective vulnerability and axonal degeneration of motor neurons in ALS pose the question of whether TDP-43 may have an additional role in the regulation of the cytoplasmic and axonal fate of mRNAs, processes important for neuron function. To investigate this possibility, we have characterized TDP-43 localization and dynamics in primary cultured motor neurons. Using a combination of cell imaging and biochemical techniques, we demonstrate that TDP-43 is localized and actively transported in live motor neuron axons, and that it co-localizes with well-studied axonal mRNA-binding proteins. Expression of the TDP-43 C-terminal fragment led to the formation of hyperphosphorylated and ubiquitinated inclusions in motor neuron cell bodies and neurites, and these inclusions specifically sequestered the mRNA-binding protein HuD. Additionally, we showed that overexpression of full-length or mutant TDP-43 in motor neurons caused a severe impairment in axon outgrowth, which was dependent on the C-terminal protein-interacting domain of TDP-43. Taken together, our results suggest a role of TDP-43 in the regulation of axonal growth, and suggest that impairment in the post-transcriptional regulation of mRNAs in the cytoplasm of motor neurons may be a major factor in the development of ALS.
Department of Cell Biology and Center for Neurodegenerative Diseases, Emory University School of Medicine, Atlanta, GA 30322, USA.
Claudia
C
Fallini
Gary J
GJ
Bassell
Wilfried
W
Rossoll
D000690:Amyotrophic Lateral Sclerosis / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D001369:Axons / Q000378:metabolism* / Q000473:pathology; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051959:ELAV Proteins / Q000378:metabolism; D000067779:ELAV-Like Protein 4; D055785:Gene Knockdown Techniques; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D009154:Mutation; D010766:Phosphorylation; D021381:Protein Transport; D012333:RNA, Messenger / Q000378:metabolism
D019208:Brain-Derived Neurotrophic Factor; D004268:DNA-Binding Proteins; D051959:ELAV Proteins; D000067779:ELAV-Like Protein 4; C498010:ELAVL4 protein, human; D012333:RNA, Messenger