The genes
glr-1 ,
nmr-1 and
nmr-2 are only a few of the predicted ionotropic glutamate receptor (GluR) -related sequences in the worm genome. We have begun to characterize more of these predicted genes with the aim of not only learning about the vertebrate genes by examining these orthologues in this simple genetic system, but going from gene to behavioral phenotype in the animal. Ultimately we hope to use smg -dependent dominant negative and RNAi strategies to achieve this end. Initially, we are examining predicted genes with defined ests which are most similar to vertebrate AMPA or Kainate receptors. In particular we have focused on sites of these which are analogous to those which control ion permeability and channel kinetics in the vertebrate GluRs, the 'editing' sites, modified post-transcriptionally by RNA editing. Similar to the
glr-1 cDNA, we have found by RT-PCR that the major cDNAs for two of these genes (K04G7.2/B0280.12, tentatively denoted
glr-2 and C06A8.9/.10,
glr-3 ) exhibit no editing of the 'Q/R' site that modulates ion permeability (1). The significance of GluR channels in the worm which might allow unimpeded influx of divalent cations remains to be determined. The kinetically important R/G site is currently being investigated. These studies have brought to light the fact that
glr-2 is the host gene for an alternative trans-spliced leader RNA operon. This gene cluster is intronically encoded, associated with an extended inverted repeat, and possibly transcribed from promoters on either genomic strand (2). In addition,
glr-2 may itself be alternatively spliced, based upon alignments of genomic and est sequences. This putative alternative splicing does not include the region carrying the trans-spliced leader genes, and is not analogous to the 'flip/flop'domain of the vertebrate GluRs. Rather, it would alter a more N-terminal domain, perhaps affecting ligand binding or other functions of this molecule. Further analysis of the genomic organization and cDNAs expressed from
glr-2 will be presented. 1)Sommer, B. et al. (1990) Science 249 : 1580-1585. 2)Ross, L. H. et al. (1995) JBC 270 : 22066-22075.