In neurodegenerative conditions such as Alzheimer's disease (AD), the tau family of proteins are displaced from their normal association with microtubules and form into paired helical filaments (PHF) that are the hallmark cytoskeletal pathology of the disease. The degree of this pathology correlates closely with the clinical severity of AD. Several posttranslational modifications of tau, including phosphorylation, have been implicated in AD pathogenesis. In addition, and importantly, actual mutations in the genes encoding human tau have recently been implicated in a variety of hereditary dementias, collectively termed frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17). This has rekindled interest in the importance of tau in neurodegenerative diseases. Despite significant progress in the field of tau biology and neurodegenerative diseases, several important issues remain unresolved. The early functional consequences of tau alterations in living neurons is incompletely understood, and it is not clear how tau in neurodegenerative diseases becomes redistributed from its normal concentration in neuronal axons to pathological inclusions in neuronal soma known as neurofibrillary tangles (NFT). One of the reasons for these gaps in knowledge is the relative paucity of model systems to study these processes. We propose to develop a transgenic model system, including germ line transmission, to study the functional consequences and trafficking patterns of human tau either mutated on sites associated with hereditary dementias or altered at select posttranslational modification sites and expressed in zebrafish neurons. Molecular biological protocols will be used to prepare normal and mutated human tau green fluorescent protein (ht-GFP) constructs under control of the neuron specific zebrafish GATA-2 promoter. The constructs are expressed after microinjection into zebrafish embryos or identified neurons later in development. Cell health, development, tau trafficking patterns and filament formation will be examined and related to both the type of tau mutation being expressed as well as to the expressed tau phosphorylation status. The overall guiding hypothesis is that the model allows dissection of a hierarchy of events relevant to potential mechanisms of neurodegenerative diseases related to critical early stages in development of disease. The model should prove very useful as well in future gene array assays to identify specific genes turned on or off at critical times in the early reorganization of FTDP-17 mutant taus identified from real time microscopic analyses. In addition, the approaches developed here will have broad usefulness in the study of functional consequences and potential genetic analyses of introducing into living vertebrate neurons other molecules involved in the pathogenesis of neurodegenerative diseases.
