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doi: 10.1242/10.1242/dev.00551

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Development 130, 3369-3378 (2003)
Copyright © 2003 The Company of Biologists Limited

The Caenorhabditis elegans ems class homeobox gene ceh-2 is required for M3 pharynx motoneuron function

Gudrun Aspöck1,*, Gary Ruvkun2 and Thomas R. Bürglin1,3,{dagger}

1 Division of Cell Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
2 Department of Molecular Biology, Massachusetts General Hospital and Department of Genetics, Harvard Medical School, Wellman 8, 50 Blossom Street, Boston, MA 02114, USA
3 Department of Biosciences at Novum, and Center for Genomics and Bioinformatics, Karolinska Institutet, Södertörns Högskola, Alfred Nobels Allé 7, SE-141 89 Huddinge, Sweden

{dagger} Author for correspondence (e-mail: thomas.burglin{at}biosci.ki.se)

Accepted 15 April 2003

Several homeobox genes, for example those of the ems class, play important roles in animal head development. We report on the expression pattern and function of ceh-2, the Caenorhabditis elegans ems/Emx ortholog. CEH-2 protein is restricted to the nuclei of one type of small muscle cell, one type of epithelial cell, and three types of neurons in the anterior pharynx in the head. We have generated a deletion allele of ceh-2 that removes the homeobox. Animals homozygous for this deletion are viable and fertile, but grow slightly slower and lay fewer eggs than wild type. We assayed the function of two types of pharynx neurons that express ceh-2, the pairs M3 and NSM. M3 activity is substantially reduced in electropharyngeograms of ceh-2 deletion mutants; this defect can account for the observed retardation in larval development, as M3 activity is known to be necessary for effective feeding. NSM function and metabolism are normal based on the assays used. All cells that express ceh-2 in wild type are present in the ceh-2 mutant and have normal morphologies. Therefore, unlike other ems/Emx genes, ceh-2 seems to be important for a late differentiation step and not for neuron specification or regional patterning. Because the CEH-2 homeodomain is well conserved, we tested whether ceh-2 can rescue ems- brain defects in Drosophila, despite the apparent differences in biological roles. We found that the C. elegans ems ortholog is able to substitute for fly ems in brain development, indicating that sequence conservation rather than conservation of biological function is important.

Key words: Caenorhabditis elegans, Homeobox, Pharynx, ceh-2, empty spiracles, Evolution, Cross-species rescue






© The Company of Biologists Ltd 2003