Formation Of Supernumerary Muscle Spindles At The Expense Of Golgi Tendon Organs In Er81-deficient Mice
Anatomy & Morphology; Developmental Biology; ETS transcription factors; expression; Golgi tendon organs; group; ia afferents; innervation; motor neurons; muscle spindles; mutant mice; myosin heavy-chain; neonatal rats; nerve growth-factor; neurotrophin-3; primary sensory neurons; proprioceptive afferents; transcription factors
ER81, a member of the ETS family of transcription factors, is essential for the formation of connections between sensory and motor neurons in the spinal cord. Mice lacking Er81 genes exhibit reduced monosynaptic sensory-motoneuron connectivity in response to muscle nerve stimulation. Proximal muscle nerve stimulation elicits fewer monosynaptic potentials than stimulation of distal nerves in hind-limbs, a deficit that is paralleled by a paucity of muscle spindles in proximal muscles (Arber et al., 2000). We examined whether a presence of spindles innervated by afferents in distal muscles correlated with the increased preservation of monosynaptic sensory-motor potentials in distal muscle nerves. Not only were spindles and Ia afferents present, but also they were supernumerary in distal muscles such as the soleus, medial gastrocnemius, and extensor hallucis longus. Concomitantly, a deficiency of Golgi tendon organs (GTOs) and Ib afferents was observed in distal muscles, as if supernumerary spindles formed at the expense of tendon organs in the absence of Er81. Thus, ER81 may be involved in mechanisms that regulate acquisition of the Ia and Ib phenotypes by subsets of proprioceptive muscle afferents. Segmental differences in muscle spindle and GTO dependence on ER81 suggest that more than one ETS transcription factor may participate in the regulation of limb proprioceptive system assembly in the mouse. (C) 2002 Wiley-Liss, Inc.
Kucera J; Cooney W; Que A; Szeder V; Stancz-Szeder H; Walro J
Developmental Dynamics
2002
2002-03
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1002/dvdy.10066" target="_blank" rel="noreferrer noopener">10.1002/dvdy.10066</a>
Neurotrophin-3 And Trkc In Muscle Are Non-essential For The Development Of Mouse Muscle Spindles
afferents; expression; growth factors; mice; muscle spindles; neonatal rats; neurons; Neurosciences & Neurology; neurotrophin-3; proprioception; transgenic mice; TrkC
NEUROTROPHIN-3 (NT3) or TrkC null mutant mice were examined for the presence of muscle spindles. Muscles of mastication, but not limbs, contained spindles in newborn and adolescent mutants. The intramuscular distribution and morphological properties of spindles in mutant masticatory muscles were indistinguishable from those of wild-type spindles. Intrafusal fibers of NT3- or trkC-deficient spindles expressed the slow-tonic isoform of myosin heavy chains, characteristic of wild-type spindles. Sensory nerve endings were observed in spindles of mutants by electron microscopy. Thus, NT3 or trkC, which is expressed in wild-type spindles, may serve functions other than those related to spindle assembly. Presumably, proprioceptive neurons innervating jaw muscles are dependent on factors other than NT3 for survival and maintenance. (C) 1998 Rapid Science Ltd.
Kucera J; Fan G P; Walro J; Copray S; Tessarollo L; Jaenisch R
Neuroreport
1998
1998-03
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1097/00001756-199803300-00026" target="_blank" rel="noreferrer noopener">10.1097/00001756-199803300-00026</a>
Sequences Of Intrafusal Fiber Formation Are Muscle-dependent In Rat Hindlimbs
Anatomy & Morphology; cat; development; Developmental Biology; embryonic-development; expression; innervation; intrafusal fibers; motor; muscle; muscle spindles; myosin heavy chains; myosin heavy-chain; neonatal rats; skeletal-muscle; slow myosin; spindles; tenuissimus muscles
A rat muscle spindle typically contains four intrafusal fibers - one nuclear bag(2), one nuclear bag, and two nuclear chain fibers. We compared the sequence of formation of the three intrafusal fiber types among the tibialis anterior (TA), soleus (SOL) and medial gastrocnemius (RIG) muscles using immunocytochemistry of spindle-specific myosin heavy chain isoforms. Spindles of the TA began to differentiate earlier and acquired the full complement of intrafusal fibers sooner than spindles of the SOL or MG muscles. At the onset of spindle assembly, the intrafusal myotubes expressed myosin heavy chains similar to those expressed by extrafusal myotubes. The first intrafusal myotube then differentiated into the bag, fiber regardless of the muscle. However, the fate of the second-forming intrafusal myotube varied among the muscles studied. It usually differentiated into a chain fiber in the TA, into a bag(1) fiber in the SOL, and into either a bag(1) or a chain in the MG. The fate of the third-forminge was reciprocal to that of the second; i.e. in those spindles in which the bag(1) fiber was second to form, a chain was third, and vice versa. The fourth and last intrafusal myotube gave rise to a chain fiber. The inter- and intramuscular variability in the fate of intrafusal myotubes of the second and third generation argues against the existence of a program intrinsic to the myotubes that would mandate their differentiation along specific paths. Rather, an extrinsic regulatory factor, probably associated with the primary afferent neuron, may govern differentiation of pluripotential myotubes into particular types of intrafusal fiber. The fate of the intrafusal myotubes might then depend on the timing of the regulatory effect of afferents relative to the stage of development of the intrafusal bundle.
Kucera J; Walro J M
Anatomy and Embryology
1994
1994-09
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00234305" target="_blank" rel="noreferrer noopener">10.1007/bf00234305</a>
Transient Expression Of A Slow-tonic Mhc Isoform By Extrafusal Fibers In The Developing Rat
Anatomy & Morphology; denervation; Developmental Biology; diversity; extrafusal fibers; intrafusal fibers; intrafusal muscle-fibers; monoclonal-antibody; motor innervation; muscle; myosin heavy-chain; neonatal rats; skeletal-muscle; slow-tonic myosin; spindles
ALD 19, a monoclonal antibody that recognizes the slow-tonic myosin heavy chain (MHC) isoform, has been used extensively as a marker for nuclear bag intrafusal fibers of muscle spindles in developing and adult rats. Extrafusal fibers of adult rat hindlimb muscles do not express slow-tonic MHC. However, while using ALD 19 to trace the fate of intrafusal fibers following neonatal denervation, we noted that some extrafusal fibers of neonates also bound this antibody. The immunolabeled extrafusal fibers were a subset of slow fibers located in the deep axial regions of crural muscles. The same fiber subset transiently displayed a weak affinity for ALD 19 during the first postnatal week in normal muscles. Denervation at birth increased the intensity of ALD 19 immunolabelling by these extrafusal fibers and extended the duration of the slow-tonic immunoreactivity into the 2nd postnatal week, after which expression diminished or ceased. Demonstration that some developing extrafusal fibers have a nerve-independent capacity for transiently expressing slow-tonic MHC, an MHC previously thought to be expressed only by intrafusal fibers, raises the possibility that both types of fiber originate from a subset of bipotential slow primary myotubes in rat hindlimbs.
Kucera J; Walro J M
Anatomy and Embryology
1993
1993-10
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00185950" target="_blank" rel="noreferrer noopener">10.1007/bf00185950</a>