Expression of the Duchenne muscular dystrophy gene products in embryonic stem cells and their differentiated derivatives.

Three protein products of the Duchenne muscular dystrophy (DMD) gene were identified so far. These include the two very similar muscle and brain type dystrophins, which are encoded by 14-kilobase (kb) mRNAs, and Dp71, which is much smaller. Dp71 is encoded by a 6.5-kb mRNA, which is transcribed from approximately 6% of the giant dystrophin gene. The present investigation shows that Dp71 is the first product of the DMD gene detectable during development. It is already expressed in the pluripotent embryonic stem cells. The two 14-kb mRNAs encoding the dystrophins are detectable only after differentiation of specialized cell types. The possible implication of these findings with regard to the ontogenetic activation and the evolution of the DMD gene are discussed.