Evolutionary change, from a gene regulation point of view, is an interesting issue in comparative developmental biology. Previous studies showed that, in Caenorhabditis elegans ,
lin-48 encodes a C2H2 zinc finger protein and it is expressed in hindgut cells, sensory neuron support cells and the excretory duct cell. We found that in C. briggsae , the C. elegans
lin-48 promoter was able to drive gfp (green fluorescent protein) expression in the same hindgut cells and neuron support cells as it does in C. elegans . However, expression in the excretory duct was essentially eliminated. This result indicates that there is a difference between C. elegans and C. briggsae in either the function or regulation of
lin-48 . To investigate the molecular nature of this difference, we have isolated the C. briggsae
lin-48 gene. Our preliminary data showed that a C. briggsae
lin-48 6 kb Sal I subclone containing the
lin-48 gene (
Cb-lin-48 ) could rescue the hindgut defects in C. elegans
lin-48 (
sa469 ) mutants. We are constructing gfp reporter transgenes to investigate the expression pattern of
Cb-lin-48 in C. elegans and C. briggsae . We have also investigated whether there is any difference in the sequence of the
lin-48 regulatory region that might be responsible for expression differences between the two species. In C. elegans ,
lin-48 requires the Pax gene
egl-38 for its expression. Two
egl-38 -responsive elements in the
lin-48 promoter (defined as
lre1 and
lre2, l in-48 r egulatory e lement 1 and 2) that are necessary for its expression have been identified.
lre1 and
lre2 are similar to the consensus sequence for Pax binding sites. By comparing the sequences, we found that two nucleotides CG in C. elegans were replaced by AA in C. briggsae
lre1, whereas
lre2 is identical in the two species. To test whether the sequence changes are responsible for the differences in
lin-48 expression in two species, we are planning to mutate the
lre1 in C. elegans promoter to the C. briggsae sequence and vice versa, and test the expression pattern of the mutant transgenes in each species. Our study on the regulation of
lin-48 in two closely related species, C. elegans and C. briggsae , will shed a light on the mechanism underlying alteration in gene expression pattern between species during the evolutionary changing process