Progesterone induction of tau phosphorylation during the differentiation of human embryonic stem cells into neuroectodermal rosettes.

Background: Tau phosphorylation is associated with neuronal division and differentiation in the fetal brain, in neuroblastoma cells, in the hibernating brains of ground squirrels and black bears, and in post-mitotic neurons in the Alzheimer's disease (AD) brain. The disassembly of the rigid microtubule structure of neurons for neuronal division and neurite remodeling requires the removal of the microtubule stabilizing protein tau via its phosphorylation. Objective: To determine if tau phosphorylation is required during neural embryogenesis. Methods: Using an Results: Tau was not expressed in hESC, but tau expression and its phosphorylation increase upon progesterone-induced differentiation of hESC into neuroectodermal rosettes. Both Cdk5 and GSK-3β, enzymes associated with tau phosphorylation, were expressed in hESCs, EBs, and neuroectodermal rosettes. The GSK-3β inhibitor LiCl, but not the Cdk-5 inhibitor roscovitine, prevented tau phosphorylation and nestin expression and the formation of neuroectodermal precursor cells. Conclusions: These preliminary results suggest that progesterone induces tau expression and its phosphorylation during the differentiation of neuroectodermal rosettes from hESC and suggest that tau and its phosphorylation is obligatory for neuronal precursor cell mitosis. The parallels between neural embryogenesis and neurodegeneration are discussed in the context of tau phosphorylation and the aberrant re-entry of neurons into the cell cycle in AD.