Reconstructing the pathway of the tensor veli palatini motor nerve during early mouse development

Abstract

The motor axons innervating the tensor veli palatini (TVP) navigate a long distance from the trigeminal motor nucleus to their target. The pathway and time course of the TVP motor nerve during this navigation process remain poorly understood. The aim of this study was to elucidate the peripheral development of the TVP motor nerve, and to confirm when the morphological relationship is established between the nerve and target muscle progenitors. Using immunohistochemistry, carbocyanine fluorescent labeling, and computerized three-dimensional image-reconstruction methods, we demonstrated the development of the TVP motor nerve in mouse embryos. Further, the morphological relationship between the extending mandibular nerve and myogenic cells stained for MyoD1 was examined. The peripheral pathfinding of the TVP motor nerve was divided into three continuous stages: (1) the earliest trigeminal motor axons leave the metencephalon and enter the primordium of the trigeminal ganglion at E9.5, when MyoD1-positive cells can already be detected in the mesenchymal core of the mandibular arch; (2) converging with the sensory root, the trigeminal motor root excites the trigeminal ganglion and begins to approach the mandibular muscle precursors at E10.5; (3) collateral branching occurs at E12.5. By E13.5, a nerve branch splits from the mandibular nerve to innervate the TVP, which appears as an individual muscle mass. These results suggest that the early process of mandibular motor nerve extension is correlated with the trigeminal ganglion cells, whereas when growing out of the ganglion, the mandibular nerve has a close relationship with target myogenic cells throughout the later process of pathway finding.

Rare case of myloglossus in Japanese cadaver: Anatomical and developmental considerations

“…Similarly, Cohen (1993) described that the masticatory compartment emerges and matures earlier than structures associated with the soft-palate field, and that the tensor veli palatini is the earliest of the palatal muscles to appear. In a murine study, Zhang et al (2000) investigated the embryological process by which the mandibular nerve innervates the tensor veli palatini. They suggested that the cells within or supporting the trigeminal ganglion express cues toward which the trigeminal motor axons grow, thereby approaching the target musculature.…”

Development of Synchronized Activity of Cranial Motor Neurons in the Segmented Embryonic Mouse Hindbrain

“…Indeed, in mouse hindbrain, the growing motor neuron axons of the mandibular branch of the trigeminal nerve initially contact the trigeminal sensory ganglion at E9.5 as they exit the hindbrain and coalesce with the sensory axons. Between E9.5 and E10.5, they make contact with the myogenic cells of their target, which surround them throughout the pathfinding process (Zhang et al . 2000).…”

Expression of Zfhep/δEF1 protein in palate, neural progenitors, and differentiated neurons

“…The size and columnar morphology of the Zfhep-positive Vm matches that observed by DiI-labeling of the trigeminal nerve at the masseter muscle (Widmer et al, 1998), emphasizing that these are differentiated neurons. In the mouse, Vm neurons are born on E9 and E10 (Taber Pierce, 1973), and axon pathfinding of Vm neurons occurs from E9.5 to E13.5 (Zhang et al, 2000), indicating that the Zfhep-positive Vm cells at E13.5 (Fig. 5O) are terminally differentiated.…”