Differential expression of muscle-specific enolase in embryonic and fetal myogenic cells during mouse development

Three isoforms of the glycolytic enzyme enolase are present in mammals and birds. During development, a switch from the alpha to the beta form takes place in skeletal muscle. In order to investigate the molecular basis of this developmental transition of enolase isoforms, we extracted total RNA from limbs of mouse embryos of different ages, and from cultures of embryonic and fetal myogenic cells. The beta message was detected in limbs from 16-day-old fetuses by Northern-blot analysis and its level was found to increase in newborn and adult muscle; no significant amount of beta mRNA was present in samples from earlier developmental stages, which did however express high levels of the muscle-specific actin mRNA. Analysis of RNA extracted from embryonic and fetal myoblasts differentiated in culture revealed that the level of beta mRNA is about 9-fold higher in fetal myotubes than in embryonic myotubes, although the level of muscle actin is comparable in both types of myotubes. These results were confirmed by S1 nuclease protection experiments. Our data show that the appearance of beta enolase transcripts temporally correlates with the formation of the second generation of muscle fibers and suggest that the developmental transition from alpha to beta enolase is linked to a developmental program which takes place in fetal but not in embryonic muscle.