The Caenorhabditis elegans gene
pes-1 encodes a transcription factor of the fork head family and is expressed during embryogenesis in the descendants of several founder cells. Animals in which
pes-1 is inactivated do not show any obvious phenotype, but a gene redundant with
pes-1, T14G12.4, has been identified (cf. abstract of S. Aslam et al. this meeting) despite the protein sequences failing to suggest that these genes are closely related. To identify putative regulatory elements in
pes-1 and T14G12.4 and to explore the evolutionary conservation of this gene pair, the C. briggsae homologues of
pes-1 and T14G12.4 were characterized. Whereas T14G12.4 is well conserved between the two species (76% identity between the sequence of the two proteins and several conserved elements outside the coding regions),
pes-1 has diverged substantially. CePes-1 and CbPes-1 proteins are only 42% identical, with 68% identity in the forkhead domain. cb-
pes-1 has two small exons extra and two of the introns are larger as compared to ce-
pes-1. Amino acid sequence duplication within CbPes-1 suggests the different gene structures may reflect rearrangements within the C. briggsae evolutionary lineage. Further rearrangements are apparent from the location of cb-
pes-1 in a strikingly gene poor region, in contrast to ce-
pes-1. Nonetheless, injection of a cb-
pes-1::gfp reporter construct into C. briggsae produced a GFP expression pattern apparently identical to the one directed by a ce-
pes-1::gfp construct in C. elegans. The expression pattern directed by a ce-
pes-1::gfp reporter construct in C. briggsae and vice versa presents some slight differences. A perfectly conserved element upstream of the first start codon of the two
pes-1 genes could identify a transcription regulating region. Whereas the ce-T14G12.4 RNAi phenotype in C. elegansis subtle (cf abstract of S. Aslam et al. this meeting), the cb-T14G12.4 RNAi phenotype in C. briggsae is more pronounced. Nevertheless, co-injection of double-stranded RNAs specific to both cb-T14G12.4 and cb-
pes-1 into wild type C. briggsae has a much stronger effect, showing that
pes-1 and T14G12.4 are also redundant in C. briggsae, although less so than in C. elegans. The reduced redundancy in C. briggsae may be linked to the different gene structures. A mutation may have lead to a reduction in the activity of Pes-1 protein in a C. briggsae ancestor, as compared to its C. eleganscounterpart such that the function came to depend mainly on T14G12.4, allowing further divergence in
pes-1 gene structure in the C. briggsae lineage. These results suggest that the overlap in function, or the redundancy, between
pes-1 and T14G12.4 can be maintained on an evolutionary time-scale.