Non-microtubule functions for maps

• Main Author: Loomis, Patricia Ann
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1994
• Subjects: Cellular biology
• ISBN: 9798208686737

The microtubule associated protein tau is composed of isoforms derived from the same gene. Tau is found predominantly within the central nervous system in association with microtubules and ribosomes. In addition, tau is the principal constituent of the neurofibrillary tangles found in the brains of patients with Alzheimer's disease and of most aged individuals with Downs syndrome (trisomy 21). We have reported in human neuroblastoma cells, the localization of tau to the nucleolar organizer regions of the acrocentric chromosomes and to their interphase counterpart, the fibrillar region of the nucleolus. Immunochemically, nuclear tau, exhibits properties similar to tau proteins found in paired helical filaments (PHFs). Like the tau in PHFs, nuclear tau cannot be extracted in standard SDS-containing electrophoresis sample buffer but requires extraction with formic acid prior to immunoblot analysis. Northern blot analysis of poly A+ mRNA isolated from cultured human cells detected a novel 2 kb tau transcript co-expressed with the 6 kb tau message. Our work suggests that the 2 kb tau message in humans may specify tau for functions not directly related to microtubules and that highly insoluble complexes of tau may play a role in normal cellular physiology. We have identified a 200 kDa protein which co-localizes with tau on the nucleolar organizer regions of the acrocentric chromosomes in cultured human cells. p200, in homology with tau, is a heat-stable, perchloric acid soluble protein which coisolates with microtubules in in vitro assays. In interphase cells, p200 localizes to the nucleolar periphery, a localization pattern which suggests p200 may interact with the filamentous nucleoskeleton as a nucleolar matrix associated protein. Utilizing the monoclonal antibody AHT-1, we detected a 400 kDa protein in various cell lines which localized to mitochondria. Interestingly, in human fibroblasts, the mitochondria appear to be preferentially associated with acetylated, stable microtubules. However, in the absence of microtubules, mitochondria and the 400 kDa protein redistribute to the intermediate filament cytoskeleton. Biochemical analyses revealed that the 400 kDa protein coisolates with microtubules in in vitro assays and may function to link mitochondria to both the microtubule and intermediate filament networks within cells.