title: Presence of embryonic myosin in normal postural muscles of the adult rat.
abstract: Indirect immunofluorescence was used to localize embryonic myosin heavy chains in soleus, adductor longus, tibialis anterior, plantaris, and extensor digitorum longus muscles of 6-month-old rats. A monoclonal antibody (2B6), specifically recognizing rat embryonic myosin, was applied to unfixed, transverse, frozen sections. The number of embryonic myosin-positive (EMP) extrafusal fibers was expressed as a percentage of the total number of fibers. EMP extrafusal fibers were only seen in the soleus and adductor longus muscles, both postural muscles. Approximately 1% of the soleus muscle fibers appeared positively stained for embryonic myosin. The majority of such fibers had a small diameter (< 500 mu2), appeared intensely fluorescent, and typically contained central nuclei. Re-expression of embryonic myosin due to spontaneous fiber denervation is not a likely factor in this study, since alpha-bungarotoxin and N-CAM localization were restricted to the motor end-plate region of EMP fibers. Since embryonic myosin was shown to disappear in all normal-sized myofibers by 2 to 3 months of age, the results suggest that the EMP extrafusal fibers seen in postural muscles of 6 to 12-month-old animals are regenerating myofibers. We speculate that a small number of muscle fibers may be regenerating in normal, adult postural muscles, in response to fiber damage possibly caused by excessive recruitment or overloading.
authors.affiliation: Graduate Program in Physical Therapy, San Francisco State University, California, USA.
authors.forename: L J
authors.initials: LJ
authors.lastname: Wanek
authors.forename: M H
authors.initials: MH
authors.lastname: Snow
mesh_terms: D000818:Animals; D005260:Female; D007150:Immunohistochemistry; D008297:Male; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism*; D009218:Myosins / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D009218:Myosins