An essential role of the neuronal cell adhesion molecule contactin in development of the Xenopus primary sensory system.

Contactin is a glycosylphosphatidylinositol-anchored immunoglobulin-like neuronal cell adhesion molecule that has been implicated in cellular interaction during development of the vertebrate central nervous system. Here we report evidence for an essential role of contactin in development of the Xenopus nervous system. Contactin mRNA is detectable by in situ hybridization in subsets of neurons in the brain, primary sensory neurons in the spinal cord, and cells along the trigeminal nerves of tailbud embryos. Contactin immunoreactivities preferentially distribute on axon tracts of the brain, the spinal cord, and the trigeminal sensory nerves. Most prominently, cell bodies and peripheral and spinal axons of primary sensory neurons, Rohon-Beard (RB) cells, are strongly contactin positive. Injection of the contactin overexpression vector into one blastomere of two-cell stage embryos leads to misdirected elongation of the peripheral axons of RB neurons in the injected half. Overexpression of antisense transcript causes depletion of contactin mRNA accumulation and abnormal development of RB neurons. In 52.3% of the injected embryos, RB neurons decrease in number and their peripheral axons in dorsal lateral tracts are defasciculated. These results demonstrate that contactin plays an essential role in development of the Xenopus primary sensory system.