Worm Breeder's Gazette 17(2): 38 (April 1, 2002)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Dept. MCD Biology and Neuroscience Research Institute, UC Santa Barbara, Santa Barbara, CA 93106
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The elt-2 and elt-7 genes have clear homologs (McGhee lab, K. Strohmaier and J.R, unpublished).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.