Worm Breeder's Gazette 12(5): 36 (February 1, 1993)
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.
The C. elegans HOM cluster contains at least four homeobox genes: ceh13 , ceh-15 / lin-39 , mab-5 ,and ceh-11 / egl-5 .To identify additional HOM genes in the cluster, we probed cosmid and YAC subclones that span the duster and extend about 200-300 kb on either side with a degenerate oligonucleotide (HB-1) that recognizes Antp-class homeoboxes (Burglin et al., 1989). Aside from the known HOM genes, this probe hybridized to a new homeobox gene about 30 kb to the right of the ceh-11 / egl-5 homeobox (on cosmid C27D11 ).This gene, designated cek-23 ,is most similar to the Drosophila genes empty spiracles (ems) and Distal-less (Dll), which are only distantly related to Antp-class homeoboxes. To find out where this gene was likely to be expressed, we constructed a ceh-23 -LacZfusion gene by using about 13 kb of genomic DNA whose 3' end terminates in the homeobox. In larvae and adults, the fusion gene was expressed prirnarily in the amphid sensilla and the CAN cells (We thank Cori Bargmann for identifying these cells).
Interestingly, Drosophila ems is required for the correct development of the antennal (olfactory) sense organs, and vertebrate ems homologs are expressed in the olfactory regions of the head. In addition, the human ems homolog, EMX-1 ,is positioned in an analogous position at the 5' end of the HOX-4 locus (E. Boncinelli, pers. comm.). The data suggest that ceh-23 ,like its homologs, may be involved in the development of olfactory neurons, and that the original HOM cluster may have contained an ems-like gene whose function has been conserved.
We did not detect other authentic homeobox genes in the cluster region, although homeoboxes that differ significantly from the probe, or that were deleted from our cosrnids or YACs, would not have been detected. It is possible that additional HOM genes may be present since certain structures along the anteroposterior axis (such as the postdeirid neuroblast and T rays) are not affected by known HOM gene mutations.