Worm Breeder's Gazette 12(3): 81 (June 15, 1992)
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.
A rudimentary version of the HOM-C homeobox cluster has been identified in C. elegans, most probably containing only four genes: ceh-13 (labial-like), ceh-15 (Deformed-like), mab-5 (Scr/Antp/Ubx/abd-A-like) and ceh-11 (Abd-B-like?)(1,2). The ceh-13 homeodomain is 68% identical to the labial homeodomain. Sequencing data from both cDNA and genomic ceh-13 clones revealed the presence of the pentapeptide TYKWM upstream of the homeodomain, which is identical to the corresponding labial pentapetide. With the help of Scott Clark we have been able to determine the direction of transcription of ceh-13 on the chromosome. It turns out that the 5' end of the ceh-13 gene is located towards ceh-15 . This is the same direction of transcription as has been found for the labial-type genes in the HOM-C complexes of D. melanogaster and vertebrates.
An 8 kb ceh-13 promoter fragment has been cloned into one of the ß-galactosidase fusion pPD vectors (3). The first exon and intron and part of the second exon of ceh-13 are included in this construct. The construct was injected into the gonads of daf-7 and rol-6 null mutants together with 150 µg/µl of cosmid DE9 ( daf-7 (+))or 200 µg/µl of pRF4 ( rol-6 (gf)). Transgenic rol-6 lines were stabilized by gamma-ray treatment with either 1900 or 3800 R. Mosaic and stable lines were monitored for ß-galactosidase expression by using either X-gal or anti-ß-galactosidase in parallel with an anti-P-granule monoclonal antibody (kindly provided by Susan Strome) to help determine the orientation of embryos. Transgenic animals for a second construct that contains only 2 kb of 5' sequences have also been obtained.
ceh-13 expression was detected as early as the 28-cell stage, which corresponds to the onset of gastrulation. The expression starts in a few cells in the posterior of the animal (excluding the very posterior, i.e. the germ line) and expands towards the anterior, but never extending towards the very anterior. Later in embryogenesis, expression appears more restricted. During larval stages, expression is restricted to the body region, to particular cells along the ventral nerve cord. These results will have to be confirmed by ceh-13 -specificantibody staining. No expression has been observed for the 2 kb construct, suggesting that important promoter elements are missing.
In Drosophila and in vertebrates, two distinct patterns of expression have been observed for labial, Hox-2 .9and GHox-2.9. In particular, during gastrulation a posteriorly located domain of transcription is observed, reminiscent of the ceh-13 early expression pattern. This apparent similarity in expression between ceh-13 and labial-type genes in vertebrates and Drosophila is intriguing. Currently we are in the process of identifying the cells expressing ceh-13 to determine whether the ceh-13 transcription is correlated with cell movement. Such a correlation has been observed for the labial-type genes during primitive streak/dorsal lip formation in vertebrates and in the dorsal ridges of Drosophila.
(2) Kenyon and Wang, Science 253, 516-517,1991
(3) Fire et al., Gene 93,189-198, 1990