Worm Breeder's Gazette 14(2): 48 (February 1, 1996)

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.

ceh-2 encodes a homologue of Drosophila empty-spiracles (ems)

Gudrun Aspöck1, Thomas R. Burglin1, Gary Ruvkun2

1 Biocenter, University of Basel, Switzerland
2 Dept. of Molecular Biology, Harvard Medical School, Boston, MA, USA

We have previously identified the homeobox gene ceh-2 *. However, the complete sequence of the homeodomain region has eluded us for a while, due to a long intron in the homeodomain. Antibodies raised against a peptide derived from the region carboxy-terminal to the homeodomain showed expression restricted to the anterior region of the pharynx**. Screening various cDNA libraries was unsuccessful. However, we succeeded in obtaining PCR bands with lambda gt11 primers and ceh-2 primers using aliquots of Pete Okkema's embryonic library (thank you for the library). Sequencing of various of these clones confirmed that we finally have the complete homeodomain. Comparison with other homeodomains shows that the Ceh-2 homeodomain is ~80 % identical to that of the Drosophila ems (83%) and the vertebrate emx genes. This poses now an intriguing puzzle: what is ceh-23 ? We had always assumed that ceh-23, although in terms of sequence simil! arity very marginally related to ems, was indeed the homologue of ems, because of its expression pattern in amphids***. The alternative suggestion that it is a Distal-less (Dll) homologue can also not true, since a bona-fide Dll exists elsewhere in the genome (~ 80% identity to the Dll homeodomain).
Perhaps, both ceh-2 and ceh-23 arose from a common ancestral gene. In flies, ems is a pattern formation gene required for anterior head development, while in vertebrates the emx genes function in the anterior brain. Perhaps ceh-2 is still functioning as a pattern formation gene in the anterior region of the head, albeit only in the pharynx, while ceh-23 has taken on the role in the nervous system.

Figure: Comparison of Ceh-2 and ems homeodomains

ceh-2   NKRIRTAFSASQLIQLEKAFEGNHYVVGNERKQLAAKLSLTETQVKVWFQNRRTKHKRVR
         ||||||||:|||:.||.|||:|:||||.|||.||..|.|.|||||||||||||||||:.
ems     PKRIRTAFSPSQLLKLEHAFESNQYVVGAERKALAQNLNLSETQVKVWFQNRRTKHKRMQ
* Bürglin et al., (1989) Nature 341, 239pp
** see WM abstract 1991
*** Wang et al., (1993) Cell 74, 29pp