New ways to look at axons in Caenorhabditis elegans

In the nematode Caenorhabditis elegans, a well-established model organism f or the analysis of nervous system development and function, nerve processes can be labelled in the intact animal with markers based on the "Green Fluo rescent Protein" (GFP). The generation of GFP variants with improved bright ness and modified emission spectra potentiated the use of this marker for i n vivo labelling of subcellular structures. This made it possible to label different groups of neurons and their axons in the same animal with GFP var iants of different spectral characteristics. Here I show with double labell ing experiments that spatial relationships of axons in small axon bundles c an now be resolved at the light microscopic level. In the future this will largely circumvent the need for time-consuming electron microscopic reconst ructions to detect local defects in axon outgrowth. Furthermore, I demonstr ate that neuronal processes can now be traced even in the head ganglia, an area of the nervous system that was previously-almost inaccessible for anal ysis due to the compact arrangement of cell bodies and axons. (C) 2000 Wile y-Liss, Inc.