ABSTRACT
Six isoforms of Tau proteins bind and stabilize microtubules via either 3- or 4- repeat regions in C-terminal (3R and 4R isoforms, respectively). Some recent researches haven showed that aberrant ratio of 3R and 4R Tau isoforms is involved the formation of tangles, which were found in brain patient with neurodegenerative disorders like Alzheimer’s disease, rather than the hyperphosphorylation of Tau proteins. Besides, this ratio may affect the differentiation, transport dynamics, distribution of mitochondria in axons of neurons. My thesis work focuses on subcellular localization and distribution of 3R and 4R Tau isoforms during the in vitro development of rat hippocampal neurons. I have also used a chip device, which can separate axons from cell bodies and dendrites. As neurons grow older, ratio of 3R to 4R isoforms declined with 3R isoforms diminishing more rapidly than the 4R isoforms increased gradually. I also examine the distribution of 3R- and 4R- Tau isoforms in the various compartments of neurons by means of fluorescence immuocytochemistry using antibodies specially recognizing these Tau isoforms. The results indicate the distribution of 3R and 4R Tau isoforms in hippocampal neurons vary as neurons grow under in vitro conditions along distinct patterns. For 3R isoforms, they appear throughout all compartments of neurons at 7 days in vitro (DIV). Gradually, 3R isoforms disappear from the dendrites and cell bodies and reside only in the axon in 21DIV neurons. On the other hand, the distribution of 4R isoforms is restricted to the cell body and proximal segments of process in 7 DIV neurons. In 14 DIV neurons, 4R isoforms are detected in all parts of neurons. At 21 DIV, 4R isoforms are again confirmed to the cell body and proximal portions of processes. By growing neurons on coverslips that contain a poly-L-lysine coated micropattern on the surface, we find that 3R isoforms residein the shafts and growth cones of the axons of the 14 DIV neurons. Interestingly, we find that 4R isoforms are highly enriched in growth cones of these axons. 4R Tau isoforms maybe play a role in highly dynamic nature of growth cones by
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controlling the dynamic of microtubule. Taken together, the results may provide us with insight about the various functions of 3R- and 4R-Tau isoforms during the course of in vitro development of rat hippocampal neurons in cultures.

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