Contactin 1 knockdown in the hindbrain induces abnormal development of the trigeminal sensory nerve in Xenopus embryos.

In Xenopus tailbud embryos, the mandibular branch of trigeminal sensory nerve has a transient pathway innervating the cement gland. This pathway is settled by pioneer neurons in the trigeminal ganglion and along which extend later-growing axons from the trigeminal ganglion and the hindbrain. Axons in this branch express a neuronal recognition molecule, Contactin 1, from the initial stage of its outgrowth in early tailbud embryos and form a tightly joined, strongly Contactin 1-positive fascicle in the later stages. When the expression vector encoding the enhanced green fluorescent protein was electrotransfected into the brain neurons of early tailbud embryos, the fluorescence was detected in the hindbrain and the trigeminal nerve at late tailbud stages. Cotransfection of antisense vector caused knockdown of Contactin 1 concurrent with defasciculation and misguidance of the sensory axons in the trigeminal mandibular branch. The results suggest that Contactin 1 is required for the growing axon of hindbrain sensory neurons to recognize and follow the pathway settled by the pioneer neurons.