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Beschreibung

Expansion of a GGGGCC hexanucleotide repeat sequence in the non-coding region of human chromosome 9 open reading frame 72 or C9orf72 (also known as ALSFTD, FTDALS, Gene ID 203228) is the most common genetic abnormality in familial and sporadic frontotemporal dementia (FTD) and motor neuron disease (MND), with amyotrophic lateral sclerosis (ALS) as the most frequent form. The number of hexanucleotide repeats in the normal population ranges from 2 to 24, whereas up to several thousand repeats (700 - 4,400 repeats) are found in the pathologically expanded allele. Unconventional repeat-associated non-ATG-initiated translation (RANT) of the GGGGCC repeats in the three alternate reading frames from both sense and antisense transcripts generates five types of dipeptide repeat (DPR) protein species, each composed of repeating units of two amino acids, glycine-alanine (GA), glycine-proline (GP), glycine-arginine (GR), alanine-proline (AP), proline-arginine (PR), respectively. Immunofluorescence localization of exogenously epxressed DPR-GFP fusions in HEK293 transfectants showed dot-like or star-shaped poly-GA inclusions with predominant cytoplasmic and occasional nuclear localization, while poly-GR and poly-PR showed large dot-like intranuclear inclusions and occasional smaller cytoplasmic inclusions. In contrast, poly-PA was evenly distributed throughout the nucleus and cytoplasm without apparent aggregation.