Cell-type-specific pattern of myc protooncogene expression in developing human embryos.

The expression of viral oncogenes in cells transformed by acutely transforming retroviruses profoundly alters proliferation and differentiation in the target cell, suggesting that the cellular homologues of the viral oncogenes, the protooncogenes, have a role in normal cell proliferation and differentiation. To investigate the possible developmental role of protooncogenes in human embryogenesis, we have determined the spatial distribution of myc gene transcripts in early human embryos by using in situ hybridization of a labeled myc exon to thin sections. The results indicate a stage- and cell-type-specific regulation of c-myc gene expression in primarily epithelial cells of late first trimester embryos. Furthermore, the data suggest that the linkage between c-myc gene expression and cellular proliferation holds for only a restricted set of embryonic cells.