Worm Breeder's Gazette 13(1): 57 (October 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.
We sequenced a cDNA, cm7b 3,which was originally identified by the random cDNA sequencing project (Waterston et al. (1992), Nature Genet. 1, 114-123), and showed that it contains a homeobox gene. This homeobox gene, ceh-20 ,is a member of the PBC class of homeobox genes and shares extensive sequence conservation with the human genes PBX1 , PBX2 and PBX3 (Burglin and Ruvkun (1992), Nature Genet. 1, 319-320). PBX1 is a proto-oncogene that was originally discovered in pre-B cell leukemias. Recently a Drosophila gene, Dpbx was identified that also has extensive sequence conservation to the PBC class (Flegel et al. (1993). Mech. Dev. 41, 155-161).
The original map location of cm7b 3was weak so we repeated the YAC hybridization and confirmed the location on YAC Y68D5 .Probing a cosmid walk from that region, we found two cosmids that hybridized with cm7b 3.Cosmid K10E10 hybridizes only with 5' probes of the cDNA, while F31E3 appears to contain the complete cDNA, thus the direction of transcription is from left to right. There are at least two introns in the gene (a 200 bp one and a 50 bp one). The map location is approximately 350-400 kb to the left of the C. elegans homeobox gene cluster. ceh-20 encodes an atypical homeodomain with 3 extra amino acids between helix 1 and helix 2 like yeast MAT-a lpha2 .In yeast and several other fungi, the mating type locus is composed of two different types of homeobox genes, a typical (aka classical) one with 60 amino acids, and an atypical one with 3 extra amino acids. We wonder now if ceh-20 and the cluster containing lin-39 , ceh-13 , mab-5 , egl-5 and ceh-23 are derived from an ancient homeobox gene cluster that originally contained only an atypical and a typical homeobox gene, similar to the organization in fungi. Consequently, the yeast/fungi mating type loci might actually be the direct evolutionary equivalents of the homeobox gene cluster.
We have generated antisera against ceh-20 fusion proteins. Antibody staining experiments show that during embryogenesis (mid-gastrulation) the gene is expressed only in the posterior half of the embryo. The staining persists during embryogenesis as the cells divide, and subsequently, during the larval stages ceh-20 is most strongly expressed in the ventral nerve cord, the retrovesicular ganglion and other neurons in the body region, such as the postderid and parts of the deirid. Weaker staining is seen in the hypodermis and muscle cells. Notably absent is staining in the nerve ring, the pharynx, the gut, and neurons in the tail ganglion. These data suggest that ceh-20 might play a role in anterior-posterior pattern formation and neurogenesis.