Figure 2:

Hypothetical model of the temporal relationship between sorting mechanisms and endogenous and exogenous tau expression. (Top row) Diagrams of endogenous tau (green) and exogenous tau (blue) distribution in a developing cultured hippocampal neuron. While tau is initially uniformly distributed throughout the cellular sphereoid and early, undifferentiated neuronal processes, sorting begins once one of the processes takes on axonal character, and is complete with the elaboration of mature postsynaptic morphology. This is dependent on two mechanisms (1) a drop in mRNA levels and new tau expression shortly after birth, and (2) the initiation of tau sorting mechanisms upon development of axonal characteristics. However, the high expression levels of exogenous tau overcome these sorting mechanisms, especially in the absence of mRNA sorting signals.