Evolutionary changes in myosin isoform expression in the tongue by quantitative PCR

Abstract

Tongue and cranial muscles experience unique mechanical demands, particularly in the complex speech of humans, and may require specialized contractile properties. Cranial muscles, derived from somitomeres, display uncommon myosin heavy chain (MHC) isoforms, including cardiac‐α (Ca) and extraocular (EOM). Tongue muscles derive from somites and do not appear to express these isoforms by protein analysis. mRNA analysis may reveal expression of Ca and EOM. We hypothesize that MHC isoform expression will reflect the functional demands on the tongue, including expression of Ca and EOM. Expression of 8 MHC isoforms in intrinsic muscles of the tongues of human, monkey, and rat were determined by QPCR. Rats express mostly 2x (67 ± 4%) with substantial 2b (31 ± 4%) and no slow MHC. Humans and monkeys express primarily conventional MHCs: 2x (20 ± 6% human, 28± 6% monkey), 2a (50 ± 7%, 58 ± 7%) and slow MHC (24 ± 6%, 10 ± 2%). The expression of faster MHC isoforms in rat than primate tongue is similar to limb MHC protein expression patterns. Of the uncommon isoforms, Ca constitutes 5 ± 3% of total MHC in humans, and individual monkey samples contained up to 7.5% EOM MHC. Neonatal and embryonic isoforms contribute less than 1% of MHC in all 3 species. We conclude that the properties of conventional MHC isoforms may not provide sufficient functional diversity for tongue action. Supported by DC05017