Expression of myogenic regulatory factors during the development of mouse tongue striated muscle.

While the role of myogenic regulatory factors (MRFs) in skeletal myogenesis has been well evaluated in limb and trunk muscles, very little is known about their role in tongue myogenesis. Here the expression of MRF mRNA in mouse tongue muscle was examined during development from embryonic day (E)11 to birth and compared them with that in hind-limb muscle. Desmin, muscle creatine kinase and troponin C mRNAs were used as markers for myoblast determination, myotubule formation and myofibre maturation, respectively. The mRNA quantities were determined by competitive reverse transcriptase-polymerase chain reaction. The expression profile of desmin mRNA indicated that myoblast determination occurred before E11 in both the tongue and hind-limb muscles; the profile of muscle creatine kinase and troponin C mRNAs indicated that myotubule formation and myofibre maturation began between E11 and 13 in both tongue and hind-limb muscles, but ended 2 days earlier in the tongue than in the hind limb. Expression of myoD and myogenin mRNAs began at E11, increased, and showed peak values earlier in the tongue muscle (E13) than in the hind-limb muscle (E15). Expression of MRF4 mRNA appeared earlier in the tongue (E13) than in the hind-limb muscle (E15) and increased in both muscles after that. These results suggest that myotubule formation and myofibre maturation in the tongue muscle progress faster than in the hind-limb muscle, a result of earlier expression of myoD, myogenin, and MRF4 in response to earlier functional demands such as suckling immediately after birth.