Regulation of acetylcholinesterase expression during neuronal differentiation.

We have examined the developmental expression of acetylcholinesterase (AChE) during the process of neuronal differentiation from a pluripotent stem cell. P19 embryonic carcinoma cells form embryoid bodies, which, when cultured with retinoic acid, are induced to differentiate into neurons and glia. No AChE activity is present in the undifferentiated stem cells, and mRNA protection analyses do not detect AChE mRNA. Commitment to a neuronal differentiation pathway results in increased levels of AChE mRNA, production of a tetrameric form of the enzyme, and secretion of AChE into the culture medium. Concomitant with subsequent morphological differentiation into neurons, enzyme secretion diminishes and AChE becomes largely tethered to the neuronal cell membranes. The enzyme is attached to the cell surface as a globular tetramer. Its hydrodynamic properties are consistent with association through a noncatalytic hydrophobic subunit rather than anchorage by a glycophospholipid tail. No change in the rate of transcription of the Ache gene was detected during the course of differentiation, suggesting that the gene is actively transcribed at very early stages of development. Results suggest that stabilization of a labile mRNA governs the increase in AChE mRNA and gene product. The studies presented indicate that an early event in neuronal differentiation is the stabilization of the mRNA leading to expression of a secreted form of AChE. A subsequent step associated with neurite outgrowth results in a transition from secretion of the tetrameric enzyme to its localization on the cell membrane.