Patrick M. Alliel

Expression of the proteoglycan SPOCK during mouse embryo development

SPOCK is a modular proteoglycan, with homology with proteins involved in cell adhesion processes and neurogenesis. We have previously shown that SPOCK transcripts predominate in the adult mouse brain. Here, we report its expression during mouse embryonic development by in situ hybridization, and immunocytochemistry. SPOCK is actively expressed at the onset of neurogenesis during periods of neuron migration and axonal outgrowth. At a later developmental stage, its expression is particularly prevalent within developing synaptic fields. In the peripheral nervous system, SPOCK expression is also developmentally regulated particularly in dorsal root ganglion neurons.

Regulated expression of the proteoglycan SPOCK in the neuromuscular system.

SPOCK is prevalent in developing synaptic fields of the central nervous system (Charbonnier et al., 2000. Mech. Dev. 90, 317-321). The expression of SPOCK during neuromuscular junction (NMJ) formation was compared to agrin and acetylcholine receptor (AChR) distribution. SPOCK is detected within the myogenic masses during the early steps of embryonic development, and distributed in the cytoplasm of myotubes before coclustering with AChRs. In the adult, SPOCK is present in axons and is highly expressed by Schwann cells. SPOCK altered expression pattern after nerve lesioning, or cholinergic transmission blockade, strongly indicate that its cellular distribution at the NMJ depends on innervation.

Neuromuscular expression of the BTB/POZ and zinc finger protein myoneurin.

Myoneurin belongs to the BTB/POZ and zinc finger protein family whose members have been implicated in regulatory functions of gene expression. Myoneurin has been identified in various tissues, but muscle is a privileged site of myoneurin gene transcription. We examined the neuromuscular expression of myoneurin during development and after axotomy. Myoneurin expression is developmentally regulated in mouse muscle and appeared to be associated with neuromuscular junctions during the late embryonic period. Myoneurin is located in and around synaptic myonuclei in mouse and human adult muscle. The expression of myoneurin is dysregulated after nerve section. Thus, the restricted myoneurin expression in synaptic myonuclei appeared to be controlled by muscle electrical activity. Myoneurin is identified within the peripheral condensed chromatin and the euchromatin/heterochromatin regions, and thus fulfills structural and expression criteria to represent a synaptic gene regulator. Muscle Nerve 29: 59–65, 2004