RESTRICTED EXPRESSION OF THE NEURONAL INTERMEDIATE FILAMENT PROTEIN PLASTICIN DURING ZEBRAFISH DEVELOPMENT

In the adult goldfish visual pathway, expression of the neuronal inter mediate filament (nIF) protein plasticin is restricted to differentiat ing retinal ganglion cells (RGCs) at the margin of the retina. Followi ng optic nerve injury, plasticin expression is elevated transiently in all RGCs coincident with the early stages of axon regeneration. These results suggest that plasticin may be expressed throughout the nervou s system during the early stages of axonogenesis. To test this hypothe sis, we analyzed plasticin expression during zebrafish (Danio rerio) n euronal development. By using immunocytochemistry and in situ hybridiz ation, we found that plasticin is expressed in restricted subsets of e arly zebrafish neurons. Expression coincides with axon outgrowth in pr ojection neurons that pioneer distinct axon tracts in the embryo. Plas ticin is expressed first in trigeminal, Rohon-Beard, and posterior lat eral line ganglia neurons, which are among the earliest neurons to ini tiate axonogenesis in zebrafish. Plasticin is expressed also in reticu lospinal neurons and in caudal primary motoneurons. Together these neu rons establish the first behavioral responses in the embryo. Plasticin expression also coincides with initial RGC axonogenesis and progressi vely decreases after RGC axons reach the tectum. At later developmenta l stages, plasticin is expressed in a subset of the cranial nerves. Th e majority of plasticin-positive neurons are within or project axons t o the peripheral nervous system. Our results suggest that plasticin su bserves the changing requirements for plasticity and stability during axonal outgrowth in neurons that project long axons. (C) 1998 Wiley-Li ss, Inc.