A surprising finding from studies of the C. elegans GATA factors has been that most occur in functionally overlapping pairs. The ectodermal GATAs ELT-5/EGL-18 and ELT-6 share overlapping function (Koh and Rothman, 2001). The GATAs MED-1,2 specify MS and E fates, END-1,3 specify E fate, and ELT-2 and ELT-7 elaborate intestinal fate in the E descendants. The availability of genome sequences for C. briggsae has enabled us to identify all the GATA factors predicted to be encoded by its genome, and in particular ask whether any are found in similar pairs as in C. elegans . The
elt-2 and
elt-7 genes have clear homologs (McGhee lab, K. Strohmaier and J.R, unpublished). The putative
elt-5/egl-18 and
elt-6 homologs are adjacent genes transcribed in the same direction, just as they are in C. elegans . We have identified a similar pair of MED-like GATA factors in C. briggsae that both appear to be encoded by a single, intronless ORF, and which both have putative SKN-1 binding sites just 5' to the coding region (properties similar to the C. elegans genes). Like
Ce-med-1 , a transgene reporter of
Cb-med-1 is expressed in the early EMS lineage in C. elegans . Unlike
Ce-med-1,2 , which are on separate linkage groups,
Cb-med-1 and -2 are adjacent to one another in an inverted, divergently-transcribed orientation. As expected from an independent, recent origin of each duplication, the predicted
Ce-med-1,2 and
Cb-med-1,2 gene products are more similar within each species than between them. The results with
end-1 and
end-3 were similar. The
end-3 gene in C. elegans is located ~30 kbp to the right of
end-1 . In C. briggsae , however, there are two
end-3 homologs a similar distance away from a single
end-1 homolog. Like
Cb-med-1,2 , the two
end-3 -like genes are adjacent, in inverted orientation and divergently transcribed. RT-PCR analysis confirmed that
Cb-end-1 and the two
Cb-end-3 genes are expressed, while cross-species transgene rescue and heat shock experiments in C. elegans shows that these genes are expressed in the E lineage, and can specify endoderm fate. Therefore, the regulation of the end genes, and the activity of their gene products, has been conserved. The high degree of sequence identity between the two C. briggsae
end-3 homologs suggests that they arose from a recent duplication, while the intra-species divergence between the
end-1,3 genes suggests that they arose from a much earlier event. We conclude that among the entire suite of C. elegans and C. briggsae GATA factors, redundancy via gene duplication arose multiple times both before and after the C. elegans/C. briggsae evolutionary split.