Model System
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          Although, primary neurons are a good model system for many aspects of the neurite outgrowth process, PC12 cell line has been chosen as most suitable model system for this study. These cells are round shaped in their undifferentiated state but in response to nerve growth factor (NGF) they differentiate extend long neurites and acquire sympathetic neuron-like phenotype (Greene L.A. and Tischler A.S. 1976.).
There are several reasons why this cell line has been chosen.
First, PC12 cells do not require addition of NGF in the culture medium for their survival which means the neurite outgrowth process can simply be switched "on" or "off" by addition/removal of this factor. They are suitable for overexpression experiments because one can wait until protein of interest builds up in the cell and then, by adding NGF, trigger neurite outgrowth.
Second, since almost all PC12 cells are round and have no neurites in culture conditions, the detection of morphological changes using microscopy is easy.
Third, they are compatible with automation and greater high-throughput screening strategy.
 

          In this study PC12 cell line stably transfected with human NGF receptor (PC12 6-15) has been used. That gives rapid response to NGF stimulation. After 24h 90% of cells have long neurites. For comparison, wild type PC12 cells develop the same phenotype only after 5-7 days of NGF stimulation (Hempstead B.L. et al. 1992.).

          To see how PC12 cells look like, how they divide and differentiate check the PC12 videos link.

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DIC images showing morphology of PC12 cells grown without addition of NGF in the culture medium. Nucleus is stained in blue.

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DIC and FC images showing morphology of PC12 6-15 cells 24h after addition of NGF in the culture medium.