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Published January 1, 1992 | Published
Journal Article Open

Induction and repression of mammalian achaete-scute homologue (MASH) gene expression during neuronal differentiation of P19 embryonal carcinoma cells


MASH1 and MASH2, mammalian homologues of the Drosophila neural determination genes achaete-scute, are members of the basic helix-loop-helix (bHLH) family of transcription factors. We show here that murine P19 embryonal carcinoma cells can be used as a model system to study the regulation and function of these genes. MASH1 and MASH2 display complementary patterns of expression during the retinoic-acid-induced neuronal differentiation of P19 cells. MASH1 mRNA is undetectable in undifferentiated P19 cells but is induced to high levels by retinoic acid coincident with neuronal differentiation. In contrast, MASH2 mRNA is expressed in undifferentiated P19 cells and is repressed by retinoic acid treatment. These complementary expression patterns suggest distinct functions for MASH1 and MASH2 in development, despite their sequence homology. In retinoic-acid-treated P19 cells, MASH1 protein expression precedes and then overlaps expression of neuronal markers. However, MASH1 is expressed by a smaller proportion of cells than expresses such markers. MASH1 immunoreactivity is not detected in differentiated cells displaying a neuronal morphology, suggesting that its expression is transient. These features of MASH1 expression are similar to those observed in vivo, and suggest that P19 cells represent a good model system in which to study the regulation of this gene. Forced expression of MASH1 was achieved in undifferentiated P19 cells by transfection of a cDNA expression construct. The transfected cells expressing exogenous MASH1 protein contained E-box-binding activity that could be super-shifted by an anti-MASH1 antibody, but exhibited no detectable phenotypic changes. Thus, unlike myogenic bHLH genes, such as MyoD, which are sufficient to induce muscle differentiation, expression of MASH1 appears insufficient to promote neurogenesis.

Additional Information

© 1992 The Company of Biologists Limited. Accepted 19 September 1991. We thank Dr. Thomas Jessell for suggesting the use of P19 cells and for providing the line, Dr. Jane Dodd for providing monoclonal antibody 5A5, Dr. Michael McBurney for helpful discussions and Dr. Scott Fraser for his time and the use of his microscope and software. We acknowledge Mr. John Montgomery for constructing the RSV expression vector, Ms. Liching Lo for cloning and analyzing MASHl-transfected P19 cells, Mr. Steven Padilla for excellent technical assistance, Ms. Rochelle Diamond for performing cell sorting, and Ms. Helen Walsh for help in preparation of the manuscript. We thank Barbara Wold, Kai Zinn, Liching Lo and Chris Schoenherr for their critical reading of the paper. JEJ was supported by an MDA postdoctoral fellowship, and KZ by an NIH postdoctoral fellowship. TS is an Associate and DJA an Assistant Investigator of the Howard Hughes Medical Institute. This work was supported in part by a Sloan Foundation Fellowship in Neuroscience to DJA, and an NSF Presidential Young Investigator Award.

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