The regenerate in the soleus bed was more susceptible to disturbance by movement due to the overlying gastrocnemius muscle, whereas that in the EDL bed was comfortably accommodated within a muscle compartment. first 4 weeks. Longer-term regenerates innervated by fast nerve suppressed STING ligand-1 fetal and slow MyHCs, retaining m-MyHC, m-MBP-C, and m-Tm, whereas fibers innervated by slow nerve suppressed fetal MyHCs and the three masticatory-specific proteins, induced slow MyHC, and showed immunohistochemical characteristics of jaw-slow fibers. We concluded that expression of m-MBP-C and m-Tm is coregulated by m-MyHC and that neural impulses to limb slow muscle are capable of suppressing masticatory-specific proteins and to channel gene expression along the jaw-slow phenotype unique to jaw-closing muscle. (J Histochem Cytochem 58:989C1004, 2010) strong class=”kwd-title” Keywords: masticatory muscle, fiber types, muscle allotype, muscle regeneration, neural influence, cat, myosin heavy chain, myosin-binding protein-C, tropomyosin Mammalian jaw and limb muscles perform different types of functions and have evolved different fiber types to match functional demands. Limb fibers may be classified into several phenotypes: slow (type I) and up to three subtypes of fast (type II) fibers, 2a, 2x, and 2b, in the order of increasing speed, which is due principally to the specific myosin isoform they express (Bottinelli et al. 1991). Slow fibers express slow (or -cardiac) myosin heavy chain (MyHC), whereas the three fast fiber types express 2A, 2X, and 2B MyHC, respectively (Bar and Pette 1988; Hoh 1992). Fast and slow muscles also express different isoforms of limb-specific myosin-binding protein-C (MBP-C) (Dhoot et al. 1985), tropomyosin (Tm), and other myofibrillar proteins (Hoh 1992). Cat jaw-closing muscles have two types of fibers with different mechanical properties (Hoh et al. 2007): masticatory fibers that express a jaw-specific myosin comprising masticatory myosin heavy chains (m-MyHCs) and masticatory light chains and jaw-slow fibers that express jaw-slow myosin comprising slow MyHCs associated with masticatory light chains (Sciote et al. 1995; Hoh et al. 2007). Recent work has shown that masticatory STING ligand-1 light chain 1 is identical to the embryonic/atrial light chain 1 (Reiser et al. 2009,2010). Masticatory fibers also express masticatory-specific isoforms of Tm (m-Tm) (Rowlerson et al. 1983) and myosin-binding protein-C (m-MBP-C), which are found in thin and thick filaments, respectively, whereas jaw-slow fibers express different isoforms of these proteins (Kang et al. 2010). Masticatory fibers are associated with a unique set of physiological properties: high Ca sensitivity (Kato et al. 1985), high force per unit cross-sectional area (Saeki et al. 1987; Toniolo et al. 2008), high tension cost (Saeki et al. 1987), moderate cross-bridge cycling rate (Hoh et al. 2007), and moderate speed of shortening (Toniolo et al. 2008). These characteristics ensure rapid development of high isometric force important for a carnivorous lifestyle. Both limb and jaw muscle fibers show physiological plasticity. Myosin composition, speed of contraction, fatigue characteristics, and other properties of fast and slow limb muscle fibers are controlled by the nerves to these muscles. When the nerves to fast and slow limb muscles are surgically crossed, the characteristics of the reinnervated muscles are reversed (Hoh 1975; Hoh et al. 1980; Pette and Vrbova 1985). When cat masticatory muscle is transplanted into a fast limb muscle bed to allow the regenerating muscle to be innervated by its nerve, the regenerated muscle expressed m-MyHC but not limb MyHCs (Hoh and Hughes 1988). However, when a masticatory muscle regenerate is innervated by the slow motor nerve, m-MyHC is initially expressed, but in the long term is replaced by slow MyHC (Hoh and Hughes 1988). The fact that regenerating cat jaw muscle innervated by a limb muscle nerve re-expresses m-MyHC suggests that jaw muscle cells are intrinsically different from limb muscles. This capacity of regenerating cat jaw muscle to express m-MyHC is independent of innervation Rabbit Polyclonal to BRP16 (Hoh and Hughes 1991b) and the basal lamina of jaw muscle (Hoh and Hughes 1991a). Myotubes derived from satellite cells of STING ligand-1 cat masticatory fibers express not only m-MyHC but also m-Tm and m-MBP-C (Kang et al. 2010) in contrast to limb muscle satellite cells, which express limb fast and slow MyHCs in culture (LaFramboise et al. 2003) but not masticatory myofibrillar proteins (Kang et al. 2010). These studies suggest that masticatory muscles belong to a distinct muscle allotype whose satellite cells are preprogrammed to express masticatory myofibrillar proteins during myogenesis. As the earlier study (Hoh and Hughes STING ligand-1 1988) on neural regulation of regenerating cat masticatory muscle used only m-MyHC as the marker for the masticatory phenotype, we investigate here whether the other known masticatory-specific proteins, m-MBP-C and m-Tm, are similarly regulated. We use IHC to study the expression of m-MyHC, m-MBP-C, and m-Tm in cat temporalis muscle regenerating under the influence of fast and slow limb muscle nerves. We show that fast muscle nerve promotes the coexpression of these masticatory myofibrillar proteins, whereas the STING ligand-1 nerve to slow muscle represses them, channeling gene expression along the jaw-slow phenotype. Materials.