Worm Breeder's Gazette 16(3): 24 (June 1, 2000)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Columbia University, New York, NY 10032
We have identified a novel family of putative cell adhesion and/or signaling molecules which are defined by the presence of a signal sequence and 2 Ig domains; none of these molecules contain a predicted transmembrane sequence, but several contain consensus sites for GPI anchorage. C.elegans contains 9 members of this family, termed the zig gene family. We hypothesize that these genes may play a role in neural patterning. As part of receptor/ligand complexes, they may be involved in cell recognition or, alternatively, they may serve as secreted and diffusible signaling molecules.
GFP fusion to the promoter region of these 9 genes reveals that 6 of these genes are expressed almost exclusively in very specific subdomains of the nervous system, while 2 of them are exclusively expressed in body wall muscles. One zig gene is expressed ubiquitously in the nervous system and in body wall muscles.
The most intriguing aspect of zig gene expression in the nervous system relates to the PVT neuron: 5 of the 9 zig genes are expressed in PVT. Aside from the panneuronally expressed zig-1 reporter gene, zig-2, zig-4 and zig-9 are expressed in few other cells than PVT, while zig-5 is expressed in about one dozen additional head neurons. PVT acts during embryonic patterning as a guidepost cell for pioneer neurons of the ventral nerve cord (Durbin, 1987) and is a source of unc-6 expression (Wadsworth et al., 1996). Given the embryonic role of PVT, we were surprised to find that at least two of the five PVT-expressed zig genes, zig-2 and zig-4, are not expressed embryonically; instead their expression is turned on right after hatching and presists throughout adulthood. Additionally, we found that maintenance, but not initiation of zig-2 and zig-4 expression requires the lim-6 LIM homeobox gene, which is expressed in PVT.
The postembryonic expression of zig-2 and zig-4 suggests that PVT subserves a postembryonic role in axonal patterning. What could this role be? In hermaphrodites relatively few neurons extend their axon into the ventral nerve cord postembryonically; however, in males, many neurons are born postembryonically in the tail and presumably require cues to extend their axon along the ventral nerve cord. We will test whether PVT plays a role in this process by driving expression of cytotoxic agents under control of the postembryonic zig-2 promoter.