Abstract
(Englisch)
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During the past year we have continued the functional analysis of the ceh-13 promoter. We focused on enh740 that drives early embryonic expression of ceh-13 in the AB lineage. In Drosophila embryos, this fragment acts as a strong wingless (wg) responsive element. In collaboration with Dr. Ralph Schnabel from the network we have tested whether enh740 may also act as a wg responsive element in the worm. We found that enh740 reporter gene expression in pop-1(RNAi) and in lit-1 mutant animals (two genes participating in an early acting wingless signalling pathway in C. elegans) is absent from most of the cells that
normally express it. Furthermore, enh740 interacts in vitro efficiently with POP-1, the only known downstream effector of all wg pathways in C.elegans. Altogether, our data provide preliminary evidence that expression of enh740 may be directly regulated by POP-1. Furthermore, our data strongly suggest that additional spaciotemporal cues are required for correct activation of ceh-13 in the early embryo. By using a combination of different methods, including deletional analysis, in vitro binding assays, comparative sequence analysis of
ceh-13 from C. elegans, C. briggsae and C. remane and a genetic screen we have started to identify these regulatory components that act in concert with the wg pathway in the activation
of ceh-13 in the early embryo.
Most of the homozygous ceh-13(lf) animals die during embryogenesis or at various larval stages and only about 3% of them reach adulthood. The three other genes in the C. elegans Hox cluster in the center of chromosome III (lin-39, mab-5 and egl-5), however, appear not to be essential and have no obvious functions during embryogenesis. The phenotypes of the corresponding null-mutants only become apparent after embryogenesis, during larval stages. Surprisingly, we found that ceh-13 interacts genetically with each of the other genes of the cluster. ceh-13(lf);lin-39(lf) double mutants exhibit a complete embryonic arrest, whereas
ceh-13(lf);mab-5(lf) and ceh-13(lf);egl-5(lf) animals die at embryonic or larval stages. These results revealed that ceh-13 shares overlapping functions with lin-39, mab-5 and egl-5 during development. Functional redundancy between ceh-13 and the other clustered Hox genes is also indicated by our finding that overexpression of LIN-39 significantly suppresses the
Ceh-13 phenotype. Using GFP reporter genes and antibody co-staining, we found that the expression domain of ceh-13 extends all along the antero-posterior axis of the worm and overlaps with that of lin-39, mab-5 and egl-5 that are expressed in distinct domains. In this
way ceh-13 may act, at least partially, redundantly with the other Hox genes thereby masking their embryonic and other essential developmental functions, that have not been detected so far in single mutants.
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