Drosophila Echinoid is an antagonist of Egfr signalling, but is not a member of the L1-type family of cell adhesion molecules

Michael Hortsch

Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, USA

(e-mail: hortsch{at}umich.edu)

Two recent articles published in Development describe the role of the Drosophila Echinoid (Ed) protein in R8 photoreceptor cell development and in Egfr signalling (Rawlins et al., 2003Go; Spencer and Cagan, 2003Go). Bai et al. first described Ed as an Ig-domain membrane protein and as an antagonist of Egfr signalling in the developing Drosophila eye (Bai et al., 2001Go). Both recent publications, which were highlighted in the `In this issue' feature, speculate that Ed might be an L1-type cell adhesion molecule (CAM). Similar to L1-type proteins, Ed is a homophilic CAM (Islam et al., 2003Go), and both proteins are members of the Ig-domain superfamily. However, Ed is not part of the L1 family and has a different protein domain structure (usually six Ig- and five FNIII-protein domains for L1-type proteins versus seven plus two for Ed). Furthermore, Ed, as well as its Drosophila paralogue Fred (Chandra et al., 2003Go), has a strikingly different cytoplasmic domain and lacks the landmark ankyrin binding site of L1-type CAMs. The Drosophila genome contains only one L1-type gene, called Neuroglian (Nrg) (Hortsch, 2000Go). Interestingly, the Nrg protein is a heterophilic ligand of Ed and triggers the Egfr antagonist activity of Ed in a synergistic manner (Islam et al., 2003Go).

REFERENCES

Bai, J., Chiu, W., Wang, J., Tzeng, T., Perrimon, N. and Hsu, J. (2001). The cell adhesion molecule Echinoid defines a new pathway that antagonizes the Drosophila EGF receptor signaling pathway. Development 128,591 -601.[Abstract/Free Full Text]

Chandra, S., Ahmed, A. and Vaessin, H. (2003). The Drosophila IgC2 domain protein friend-of-echinoid, a paralogue of echinoid, limits the number of sensory organ precursors in the wing disc and interacts with the Notch signaling pathway. Dev. Biol. 256,302 -316.[CrossRef][Medline]

Hortsch, M. (2000). Structural and functional evolution of the L1-family: are four adhesion molecules better than one? Mol. Cell. Neurosci. 15,1 -10.[CrossRef][Medline]

Islam, R., Wei, S.-Y., Chiu, W.-H., Hortsch, M. and Hsu, J.-C. (2003). Neuroglian activates Echinoid to antagonize the Drosophila EGF receptor signaling pathway. Development 130,2051 -2059.[Abstract/Free Full Text]

Rawlins, E. L., White, N. M. and Jarman, A. P. (2003). Echinoid limits R8 photoreceptor specification by inhibiting inappropriate EGF receptor signalling within R8 equivalence groups. Development 130,3715 -3724.[Abstract/Free Full Text]

Spencer, S. A. and Cagan, R. L. (2003). Echinoid is essential for regulation of Egfr signaling and R8 formation during Drosophila eye development. Development 130,3725 -3733.[Abstract/Free Full Text]





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