ACTIVATION OF MUSCLE GENES WITHOUT MYOGENESIS BY ECTOPIC EXPRESSION OF MYOD IN FROG EMBRYO CELLS

THE sequence-specific DNA-binding protein, MyoD1,2, can acti-vate muscle-specific gene expression in some cells in culture13,4. Xenopus MyoD (XMyoD) transcription is activated as a con-sequence of mesoderm induction in the early myotomes5, from which the axial musculature develops. XMyoD RNA accumulates about two hours before muscle-specific actin transcripts first appear5, and so is expressed at the right time and in the right place to play a part in activating muscle-specific gene expression in normal development (but see ref. 6). To test this idea, we have expressed XMyoD ectopically in early Xenopus embryos. We find that injection of XMyoD RNA can strongly activate muscle genes in embryo cells normally destined to form ectoderm. Nevertheless, these cells fail to differentiate as muscle, suggesting that additional factors are required for complete and stable myogenesis. © 1990 Nature Publishing Group.