TRANSCRIPTIONAL ACTIVITY OF THE NEURON-SPECIFIC ENOLASE (NSE) PROMOTER IN MURINE EMBRYONIC STEM (ES) CELLS AND PREIMPLANTATION EMBRYOS

Mouse embryonic stem (ES) cells were transfected with a plasmid compos ed of an E. coli lacZ gene fused to 1.8 kb of rat neuron-specific enol ase (NSE) promoter sequences. While this reporter construct had been s hown previously to function exclusively in postmitotic neurons and neu ro-endocrine cells of transgenic mice, stably transfected ES cell clon es unexpectedly displayed beta-galactosidase (beta-Gal) activity in th e undifferentiated state. This transcriptional activity of the heterol ogous NSE promoter was confirmed by the identification of endogenous N SE mRNA in undifferentiated ES cells, mouse morulae and blastocysts. N SE protein, however, could not be found in undifferentiated ES cells. Interestingly, in ES cells which were cultured for 7 days under differ entiation conditions in vitro, beta-Gal activity decreased to basal le vels consistent with the parallel down-regulation of endogenous NSE mR NA. In contrast, prolonged culture of ES cells under differentiation c onditions led to the reappearance of NSE mRNA and beta-Gal activity af ter 17 days. Significant increases in beta-Gal activity were also obse rved in ES cells which were cultured either on dishes coated with atta chment factors such as laminin and gelatin or in the presence of nerve growth factor (NGF). These results suggest that i) transcriptional co ntrol mechanisms regulating neuronal gene expression are present at ea rly developmental stages in the mouse and ii) ES cells provide a usefu l in vitro model system for the analysis of developmentally regulated cellular and molecular events coupled to neuron-specific enolase promo ter activity.