Hexanucleotide repeat expansion in C9ORF72 is the most frequent cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we demonstrate that the repeat-associated non-AUG (RAN) translation of (GGGGCC) n -containing RNAs into poly-dipeptides can initiate in vivo without a 5'-cap. The primary RNA substrate for RAN translation of C9ORF72 sense repeats is shown to be the spliced first intron, following its excision from the initial pre-mRNA and transport to the cytoplasm. Cap-independent RAN translation is shown to be upregulated by various stress stimuli through phosphorylation of the alpha subunit of eukaryotic initiation factor-2 (eIF2alpha), the core event of an integrated stress response (ISR). Compounds inhibiting phospho-eIF2alpha-signaling pathways are shown to suppress RAN translation. Since the poly-dipeptides can themselves induce stress, these findings support a feedforward loop with initial repeat-mediated toxicity enhancing RAN translation and subsequent production of additional poly-dipeptides through ISR, thereby promoting progressive disease.

Multiple sclerosis is considered a disease of myelin destruction; Parkinson's disease (PD), one of dopaminergic neuron depletion; ALS, a disease of motor neuron death; and Alzheimer's, a disease of plaques and tangles. Although these disorders differ in important ways, they also have common pathogenic features, including inflammation, genetic mutations, inappropriate protein aggregates (e.g., Lewy bodies, amyloid plaques), and biochemical defects leading to apoptosis, such as oxidative stress and mitochondrial dysfunction. In most disorders, it remains uncertain whether inflammation and protein aggregation are neurotoxic or neuroprotective. Elucidating the mechanisms that orchestrate neuronal diseases should facilitate development of neuroprotective and neurorestorative strategies.

Tubulin purified by phosphocellulose chromatography and free of accessory proteins will not form microtubules in the absence or presence of microtubule initiating sites (flagellar microtubules). The capacity for growth onto pre-existing "seeds" can be restored by the addition of small quantities of partially purified tau protein. Larger quantities restore the capacity for spontaneous assembly. These results suggest that tubulin requires tau for both initiation and growth of microtubules and that tau is incorporated into the microtubule throughout its length.