Previous studies have shown that C. elegans ovo-related gene
lin-48 expresses in a small number of cells including the excretory duct cell. In the related species C. briggsae, the expression is conserved in all cells except the excretory duct. This
lin-48 expression difference affects excretory duct morphogenesis. In C. briggsae, as well as in C. elegans
lin-48(
sa496) mutants, the excretory duct is more anterior than in C. elegans wild type. This indicates that C. elegans
lin-48 (
Ce-lin-48) is involved in duct morphogenesis and positioning, but this gene function is absent in C. briggsae (1). We have made reporter transgenes composed of the
lin-48 regulatory sequences from C. elegans or C. briggsae driving expression of green fluorescent protein (GFP). Tests of these clones in each species showed that only the
Ce-lin-48 is expressed in excretory duct cell in C. elegans animal. These results indicate that there are differences in both cis-regulatory sequences and trans-acting proteins between the two species. By creating chimeric reporter transgenes including C. elegans and C. briggsae regulatory sequences, we have found that one difference between the two species is the presence of regulatory sequences in
Ce-lin-48 that respond to the bZip protein CES-2 (1). The
lin-48 gene expression differences between C. elegans and C. briggsae could result from loss of excretory duct expression in the C.briggsae lineage or acquired expression in the C. elegans lineage. To distinguish between these possibilities, we have analyzed three additional Caenorhabditis species (C. remanei, C. sp. CB5161 and C. sp. PS1010). We found these species have a duct morphology similar to C. briggsae indicating the C. elegans morphology is unique to this species. For comparison to C. elegans and C. briggsae, we have isolated the
lin-48 gene from C. remanei and C. sp. CB5161. Alignment of the
lin-48 regulatory sequences reveals that the sequences are more conserved among C. briggsae, C. remanei and C. sp. 5161. Several conserved domains are absent from C. elegans, whereas the previously identified CES-2 binding sites are absent from the other species. Currently, we are creating
lin-48::gfp reporter transgenes for each species to observe the gene expression patterns. Further experiments with these transgenes will allow us to test whether the differences between C. elegans and the other species result from a loss of repressor elements or gain of activator elements in the C. elegans gene. (1)X. Wang and H. M. Chamberlin (2002) Genes & Development 16: 2345-2349.