Worm Breeder's Gazette 14(5): 46 (February 1, 1997)

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.

Cetwist-like1, a novel basic helix-loop-helix protein that is active in the M lineage

Brian Harfe1, Andrew Fire2

1 The Johns Hopkins University Biology Graduate Program, The Carnegie Institution of Washington
2 The Carnegie Institution of Washington

        The C. elegans genome project recently revealed the coding
region for a novel basic helix-loop-helix (bHLH) factor that is similar
to the twist family of transcription factors. In other systems (flies,
vertebrates), the twist transcription factor is important in determining
different types of muscle fate; twist protein is thought to interact
with other muscle specific transcription factors to modulate muscle gene
        To begin to understand the role of the new C. elegans bHLH gene
we have done the following:
1. Identification and sequencing of a cDNA clone from a phage library.
This indicates that the gene is expressed and allowed definitive
assignment of the intron-exon boundaries. Inside the bHLH domain, the C.
elegans gene shares 61% identity to insect twist and 59% identity to
mouse and Xenopus twist (Fig.1). This identity is much closer to twist
members in other species then to other C. elegans bHLH genes. 
        The twist family is not well conserved outside of the bHLH
domain, but all published twist genes have three distinct features. a)
Each starts with two Met codons. b) Each has a small conserved domain
just 3' of the bHLH domain. c) Each ends just after the 3' conserved
domain. The C. elegans gene has none of these features. We are therefore
tentatively calling the C. elegans factor Cetwist-like1.
2. Characterization of the regulatory sequences using lacZ and gfp gene
fusions and tagging constructs. Both reporter fusions and gfp tagged
constructs yielded a similar expression pattern (Fig.2). The
Cetwist-like1 promoter is active in the M mesoblast in 3-fold stage
embryos and in all M descendants until there are 16 such cells. Promoter
activity is then turned off in the 14 M-derived body wall muscle cells
but remains on in the two SM's and post-embryonic coelomocytes. Reporter
expression can be seen in all the descendants of the SM's until the L4
to adult transition. In addition, reporter activity is seen in the 4
embryonic coelomocytes.
        Preliminary deletion analysis of the promoter has determined
that there are distinct 5' signals for the M lineage and the
coelomocytes. Future plans include making a mutation in the
Cetwist-like1 gene and determining how this protein interacts with other
muscle specific transcription factors like MyoD (Chen et al. Development
120:1631-1641, 1994) and CEH-24 (Fire and Harfe, WBG 13(4): 91, 1994).