Differential expression of troponin C genes during tongue myogenesis

Abstract

Determination of muscle fiber type is related to the developmental stage of the tissue. Ordinarily the final distribution of fast and slow fibers in a muscle is determined postnatally. Tongue muscle, however, is composed solely of fast-twitch fibers that express only troponin C fast mRNA and fast (type II) myosin heavy chain (MHC) proteins in both the adult and the one-dayold mouse. The fiber-type determination of this muscle was examined during fetal development. Both troponin C fast and slow mRNAs were expressed at initial stages of tongue development at embryonic day 13. However, by embryonic day 16 the troponin C fast transcripts predominated. At 17 days of embryonic development, TnC fast mRNA was 10 times more abundant than TnC slow, and at 18 days of development the TnC slow mRNA was barely detectable. The tongue muscle myotubes expressed fast, slow, and embryonic MHC isoforms during early embryonic development. At 18 days of gestation, the MHC isoform expressed by the majority of the myotubes was the fast isoform, whereas the slow isoform was present in very few fibers. RT-PCR analysis of the MHC transcripts present throughout tongue development demonstrated expression of the mdms or type IIx MHC in both late fetal and postnatal stages of development. In contrast, the type I/b slow MHC mRNA was undetectable in the postnatal and adult tongue. The absence of TnC and MHC slow-isoform mRNAs in the newborn mouse tongue suggests that slow isoform genes become dominantly repressed with the TnC-F and MHC type IIx genes remaining transcriptionally active, giving rise to an unusually homogeneous fast-twitch phenotype. The tongue muscle fibers acquire their specific adult-type fiber characteristics during fetal development rather than postnatally. Dev. Dyn. 209:36-44, 1997. r 1997 Wiley-Liss, Inc.

Molecular Regulation of Tongue and Craniofacial Muscle Differentiation

“…The acquisition of a homogeneously fast adult fiber-type occurs prior to birth in the developing tongue. Slow isoforms of MHC-slow and TnC-slow are both transcriptionally down-regulated before birth (Dalrymple et al, 1999;Prigozy et al, 1997). We have also observed post-transcriptional regulation of a fiber-type-specific isoform, MHC-slow (Dalrymple et al, 1999).…”

“…We have been able to determine that the predominant expression of Myf-5 in the developing murine tongue bears strong similarity to that in other muscles that are Myf-5-specified (Prigozy et al, 1997;Kablar et al, 1998;Dalrymple et al, 1999). However, the partial deleterious phenotypes that arise in the tongue muscle when myoblast migratory events are inhibited suggest that there is a cell lineage that may be unaccounted for in the tongue (Epstein et al, 1996;Tajbakhsh et al, 1997).…”

“…Analysis of current data gathered regarding tongue myogenesis suggests that its profile of MRF expression is distinct from that of the limb (Ontell et al, 1993;Dalrymple et al, 1999). Moreover, the developing tongue muscle has been shown to attain its adult fast-fiber phenotype prior to birth (Prigozy et al, 1997). Acquisition of its phenotype is associated with a complement of fiber-type and developmentally specific genes that are also expressed in a fashion different from the limb (Dalrymple et al, 1999).…”

“…The final maturation events in both post-natal muscle and adult muscle are strongly affected by both nerve and functional activity-dependent events (Buonanno and Rosenthal, 1996;Buonanno et al, 1998;Chin et al, 1998). In muscles, such as the tongue, that possess a mature adult phenotype prior to birth, the question of fiber-type acquisition becomes increasingly complicated (Prigozy et al, 1997;Dalrymple et al, 1999). Active skeletal muscles are capable of responding to both environmental stresses and pathologic conditions by altering their fiber-type composition.…”

“…Fast fibers are defined as alkali-stable with increased ATPase activity and increased shortening velocity, while slow fibers are defined as acid-stable with decreased ATPase activity and thus decreased shortening velocity (Swynghedauw, 1986;Pette and Staron, 1990). The analysis of the tongue musculature has shown that it is uniformly composed of fast fiber types (Brozanski et al 1993;Prigozy et al, 1997;Dalrymple et al 1999).…”