Extracellular Muscle Myosin II Promotes Sensory Axon Formation

Abstract

Myosin II is an intracellular force-generating enzyme with no known extracellular action. In the course of experiments involving trituration loading of skeletal myosin II into embryonic sensory neurons we observed that extracellular application of myosin II to neurons resulted in a robust increase in the number of axons initiated by each neuron, but did not alter the rate of axon extension. Substratum bound myosin II in the presence of laminin was sufficient to elicit increases in axon formation. However, in the absence of laminin, extracellular myosin II alone was not sufficient to promote axon formation, although it allowed neuron survival in the presence of neurotrophin. Myosin II promoted the attachment of neurons to the substratum in the absence or presence of laminin. In addition to promoting the initiation of axons, extracellular myosin II also increased the frequency of axon collateral branching. Finally, extracellular myosin II did not affect growth cone collapse in response to semaphorin-IIIA, but attenuated the inhibitory action of chondroitin sulfate proteoglycans on axon extension. Surprisingly, these results demonstrate that extracellular myosin II promotes attachment of neurons and increases axon formation and branching. The potential significance of these observations is discussed in the context of myosin II release from injured muscle and a previous demonstration of extracellular myosin II association with the extracellular matrix.

Axon extension in the fast and slow lanes: Substratum‐dependent engagement of myosin II functions

“…Cell attachment assays were performed as previously described (Silver and Gallo, 2005) and the number of attached neurons was determined by staining coverslips with neuron-specific bIII tubulin antibodies. Briefly, cells were plated in parallel on coverslips coated with laminin or polylysine for 3.5 h. The medium was then removed and the coverslips were washed three times to remove nonadherent cells by adding and removing 1 mL of fresh culture medium, allowing the medium to run over the coverslip.…”

The Effects of Target Skeletal Muscle Cells on Dorsal Root Ganglion Neuronal Outgrowth and Migration In Vitro

“…Peripheral nerve recovery after crush injury was suppressed by chronic inflammation in peripheral target tissue [11]. Extracellular application of myosin II or skeletal muscle extract to neurons resulted in a robust increase in the number of axons initiated by each neuron or the number of survival neurons [12]–[13]. Sensory nerve cross-anastomosis (sensory protection) provides a modified trophic environment by modulating neurotrophic factor synthesis in muscle [14].…”

Neuronal Phenotype and Tyrosine Kinase Receptor Expression in Cocultures of Dorsal Root Ganglion and Skeletal Muscle Cells

“…Sensory neurons lost in the absence of target‐derived trophic support should be rescued by treatment with muscle extract or neurotrophic factors which are known to be required for the survival of these neurons (Snider,1994; Caldero et al,1998). Extracellular application of skeletal myosin II to embryonic sensory neurons resulted in increasing axon formation and branching in each neuron in vitro (Silver and Gallo,2005). It has been shown that the increase in excitability of skeletal muscle is regulated by the excitatory afferents in the spinal cord‐DRG‐skeletal muscle organotypic coculture system (Streit et al,1991).…”