ZEBRAFISH NEURONS EXPRESS 2 L1-RELATED MOLECULES DURING EARLY AXONOGENESIS

Partial clones coding for two L1-related genes, zebrafish L1,1 and L1, 2, were isolated from a zebrafish embryonic cDNA library. The homology analysis, based on the deduced amino acid sequences of L1.1 and L1,2, revealed that the two molecules are most closely related to each othe r and to mouse L1. Analysis by in situ hybridization revealed that dur ing embryonic development of the nervous system the L1.1 and L1,2 mess ages are restricted to postmitotic neurons and that the onset of expre ssion correlates with the initiation of axonogenesis. L1,1 is expresse d by all known classes of neurons, consistent with an important genera l function during axonal outgrowth. Most of the neurons also express 1 ,1,2. However, 1,1,2 either is undetectable or is expressed at very lo w levels in the neurons of the olfactory placodes, anterior lateral li ne/acoustic ganglia complex, posterior lateral line ganglion, and in l ate developing hindbrain neurons. In the spinal cord, L1,2 message is detected only in a subpopulation of Rohon-Beard cells. This suggests t he possibility that different levels of L1,2 expression may serve to d istinguish different populations of neurons and their axons. (C) 1995 Wiley-Liss, Inc.