Worm Breeder's Gazette 15(2): 28 (February 1, 1998)
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.of MCD Biology, University of Colorado, Boulder, CO 80309-0347
Previously, we reported using representational difference
analysis (RDA) to identify candidate nob-1 genomic and cDNA clones (1).
nob-1 resided in one of the remaining gaps in the physical map on LGIIIR
and therefore, was not clonable by conventional means. Sequence
analysis of the 5' tag of each of two candidate cDNA clones revealed no
significant matches to any sequences in either the C. elegans genomic
databases or in Genbank. However, sequence analysis of the 3' end of
these clones revealed that these cDNAs can encode a
homeodomain-containing protein most similar to those of the posterior
paralog group containing Abd-B and the vertebrate Hox 9-13 genes.
Alignment of these sequences (see Figure) is shown opposite and includes
the ten best matches as well as Abd-B and egl-5, another C. elegans
gene with similarity to the posterior paralog group. Like other members
of this group, the predicted nob-1 protein lacks an N-terminal
hexapeptide found in more anteriorly-expressed Hox genes and contains
three residues highly conserved amongst members of this group (2) at
positions 3, 7, and 10 (shown with asterisks). RNA blot analysis with
one of these cDNAs demonstrates that a major transcript of 1.2 kb is
detected at all stages of development, consistent with nob-1's role in
embryonic and post-embryonic development (3,4). Less abundant
transcripts of 2.3 kb and 700 bp are also detected and may be
developmentally regulated.
Phenotypic analyses on embryos homozygous for the severe
loss-of-function allele, ct223, suggested that while nob-1 is not
required for proper execution of posterior cell lineages, it is needed
late in embryogenesis to properly specify fates of posterior gut,
neurons, and hypodermis (3,4). Identification of candidate nob-1 cDNAs
with similarity to posteriorly-expressed Hox genes is consistent with
this interpretation. We are intrigued by the similar phenotypes
produced by severe loss-of-function mutations in ceh-13, a C. elegans
labial homolog (5), and nob-1. While mutations in each of these genes
result in morphological defects in the anterior and posterior,
respectively, neither of the mutations appears to have any effect on the
embryonic lineage. This suggests that in C. elegans, the two Hox genes
essential for embryogenesis are not required for specifying the lineage,
but instead for proper execution of region-specific differentiation.
Our next experiments are directed towards characterizing the molecular
lesions in each of three nob-1 alleles and determining its expression
pattern. In addition, we are analyzing YACs in this region to determine
if nob-1 is an orphan Hox gene, or if there is another sister Hox
cluster on the right arm of LGIII.
1. Weaver, D. C., Van Auken, K., and B. Wood. (1997). Worm Breeder's
Gazette. 15 (1). p.29
2. Gehring, W. J., Affolter, M., and Burglin, T. (1994). Homeodomain
Proteins, in Annu. Rev. Biochem., 63:487-526.
3. Van Auken, K., Edgar, L., and B. Wood. (1996). West Coast Worm
Meeting Abstract, p.19.
4. Van Auken, K., Edgar, L., and B. Wood. (1997). International C.
elegans Meeting Abstracts, p.198.
5. Brunschwig, K., Wittmann, C., Schnabel, R., Tobler, H., and Muller,
F. (1997). Worm Breeder's Gazette. 15 (1). p.47.