Worm Breeder's Gazette 15(3): 18 (June 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.

Activation of Ceh-14 through C. elegans Ldp: An evolutionary conserved process

G. Cassata, H. Kagoshima, T.R. Burglin

Dept. of Cell Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 BASEL, Switzerland

        The transcription factor Ceh-14 is a member of the LIM class of
homeobox genes, which contain two tandem LIM domains and a homeodomain.
It has been shown that the LIM domains (zinc binding structures similar
to Zinc fingers) are preventing the homeodomain from binding DNA. The
LIM domains themselves are protein-protein interaction domains. Proteins
specifically binding LIM domains were cloned and shown to activate the
DNA binding of the homeodomain (Agulnik et al. Nature 384, 1996,
270-72). The LIM interacting proteins (Ldp) are very well conserved
between different animal phyla.
        An Ldp homologue with two splice variants has been uncovered by
the C. elegans genome project (C.e. ldp-1a and 1b). To understand
whether the activation of Ceh-14 is accomplished by C.e. Ldp-1 we
performed a yeast two hybrid assay. Using the Ceh-14 tandem LIM  domains
as a bait (fused to the GAL4 DNA binding domain) we showed that both
splice variants of C.e. Ldp-1 (fused to GAL4 activation domain) bind the
Ceh-14 tandem LIM  domains (Fig. 1). To control the specificity of the
binding we changed crucial cysteine residues to serine, which is very
similar sterically, but cannot bind the zinc ion and thus cannot
participate in forming the ternary complex with the other three
residues. The metal binding is essential for the tertiary structure (
Kosa et al. Biochemistry 33, 1994, 468-77). Point mutations of this type
in either LIM domain abolish the interaction with Ldp-1 (Fig. 1).
Furthermore we showed that the interaction between LIM and Ldp's  is
conserved between C. elegans and vertebrates since Xenopus Ldp (clone
kindly provided by Dr. Alan Agulnik) can also specifically bind Ceh-14
(Fig. 1). We are now examining the expression pattern of C.e. ldp-1
using promotor-gfp  constructs. Although detailed identification of the
cells expressing C.e. ldp-1 remains to be done, we observe coexpression
of ceh-14 and ldp-1. Furthermore ldp-1 is expressed in most neuronal and
non-neuronal cells in which other LIM homeobox genes are known to be