An Immunocytochemical Marker For Early-type-i Muscle-fibers In The Developing Rat Hindlimb
Anatomy & Morphology; Developmental Biology; expression; extrafusal; fibers; isoforms; mhc isoforms; muscle development; myosin heavy-chain; myotubes; skeletal-muscle; slow myosin; slow myosins; type i fibers
Muscle fibers develop sequentially from several generations of myotubes that express specific isoforms of myosin heavy chain (MHC). We observed that the chicken-derived monoclonal antibody (mAb) S46 binds to myotubes of the fetal rat hindlimb in a specific temporal and spatial pattern. To determine the type and fate of the S46-reactive myotubes, we immunoreacted sections of fetal, neonatal and postnatal hindlimb muscles to this antibody. The mAb S46 bound to a subpopulation of primary myotubes in the tibialis anterior, and to all primary and slow/fast secondary myotubes in the soleus muscle. The S46-reactive primary myotubes represented the oldest set of myotubes in the muscles. Reactivity to S46 was present from the earliest stages of muscle development, peaked in the late fetal period, and dissipated in the first postnatal week, suggesting that mAb S46 binds to a developmental form of slow myosin. The regional distribution of myotubes that bound S46 in fetal muscles was identical to the distribution of type I (slow-twitch) fibers in the adult, indicating that S46-reactive myotubes ultimately develop into type I extrafusal fibers. Thus, mAb S46 can be used as a marker for prospective type I extrafusal fibers in the rat hindlimb.
Kucera J; Walro J M
Anatomy and Embryology
1995
1995-08
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00186002" target="_blank" rel="noreferrer noopener">10.1007/bf00186002</a>
Origin Of Intrafusal Fibers From A Subset Of Primary Myotubes In The Rat
afferents; Anatomy & Morphology; development; Developmental Biology; developmental myosins; expression; intrafusal fibers; isoforms; muscle; muscle spindles; muscle spindles; myosin heavy chains; myosin heavy-chain
S46, a monoclonal antibody (mAb) specific for the SM-1 and SM-2 isoforms of avian slow myosin heavy chains (MHC), was used to study the earliest stages of development of intrafusal fibers in muscle spindles of the rat hindlimb. Spindles formed only in the regions of fetal muscles that contained primary myotubes reactive to mAb S46, such as the axial region of the tibialis anterior muscle. The first intrafusal fiber to form, the nuclear bag, fiber, originated from within the population of S46-reactive primary myotubes. Binding of mAb S46 by myotubes giving rise to the bag, fibers preceded the appearance of encapsulated spindles in the muscles by electron microscopy. However, reactivity to S46 intensified in the myotubes transforming into bag, fibers after the innervation of the fibers by afferents, and dissipated in myotubes differentiating into slow-twitch (type I) extrafusal fibers. Thus, afferents may enhance intrafusal expression of the MHC isoform reactive to mAb S46. The pattern of S46 binding to nuclear bag and chain intrafusal fibers in both developing and adult spindles was the same as that reported for the mAb ALD19, suggesting that both antibodies bind to the same MHC isoform. This isoform is probably a developmental form of slow myosin, because it was transiently expressed during the development of type I extrafusal fibers. The origin of bag, intrafusal and type I extrafusal fibers from a bipotential subpopulation of primary myotubes reactive to mAb S46 correlates with the location of muscle spindles in the slow regions of muscles in adult rat hindlimbs.
Kucera J; Walro J M
Anatomy and Embryology
1995
1995-08
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00186003" target="_blank" rel="noreferrer noopener">10.1007/bf00186003</a>