Figure 5. A model for the molecular cascade resulting from the C9orf72 HRE structural polymorphism.
The DNA and RNA•DNA structures formed in the GGGGCC repeat region impede RNA polymerase transcription, which results in transcriptional pausing and abortion. This leads to a loss of full-length products and an accumulation of abortive transcripts. Abortive transcripts that contain the hexanucleotide repeats form G-quadruplexes and hairpins and bind essential proteins in a conformation-dependent manner. Sequestration of these proteins leads to nucleolar stress and other downstream defects. The repeat-containing transcripts can also escape the nucleus and be bound by ribosomal complexes, thereby increasing repeat-associated non-ATG-dependent translation that results in aggregative polydipeptides.