[
Biochem Biophys Res Commun,
2003]
The EMI domain, first named after its presence in proteins of the EMILIN family, was identified here in several metazoan proteins with various domain architectures, among which the mammalian NEU1/NG3 proteins and Caenorhabditis elegans CED-1, identified as a transmembrane receptor that mediates cell corpse engulfment. Functional data available for EMILIN proteins suggest that the EMI domain could be a protein-protein interaction module. Sequence profiles specific of the EMI family of domains led to identify the probable orthologs of the C. elegans CED-1 protein in mammals and insects, which were yet uncovered.
[
International C. elegans Meeting,
2001]
Chemotaxis and thermotaxis, the two sensory mechanisms that C. elegans uses to interact with its environment have been reported in detail. However little is known of phototaxis, another operative sensory mechanism. To investigate photoresponse in the worm, we used two approaches. In (1), phototaxis of wild type worms were observed on NGA plates using two different light sources and (2) photoresponse of a single worm was determined under limited light conditions. Phototaxis is shown as phototaxis rate (PR) = Number of worms in area after irradiation/ worms before irradiation. In 30 independent assays using white light, PR ranged between 3.0 and 0.8. Using a thermostat filter to maintain constant temperature, PR decreased to between 1.35 and 0.75. This result indicates that the worm is sensitive to temperature increase during irradiation. We are yet to obtain clear results with a light source of 533 nm filter and we are trying other approaches for precise determination. Photoresponse was observed after irradiation shift from weak to strong light and percentage of responsive animals were classified as avoidance, weak avoidance and no response. In 15 independent tests, 25% of the worms responded to irradiation. Using mutant worms of chemotaxis and thermotaxis, the percentage irradiation response was decreased proportionally to the morphology of the amphid cilia. This suggests that some molecules in the amphid cilia could respond to light. The relationship between phototaxis and photoresponse and its link to chemotaxis and thermotaxis are still underway.
[
Genes Dev,
2012]
During apoptosis, apoptotic cells are removed by professional phagocytes or neighboring engulfing cells either directly through phagocytic receptors or indirectly through bridging molecules that cross-link dying cells to phagocytes. However, how bridging molecules recognize "eat me" signals and phagocytic receptors to mediate engulfment remains unclear. Here, we report the structural and functional studies of Caenorhabditis elegans TTR-52, a recently identified bridging molecule that cross-links surface-exposed phosphatidylserine (PtdSer) on apoptotic cells to the CED-1 receptor on phagocytes. Crystal structure studies show that TTR-52 has an open -barrel-like structure with some similarities to the PKC-C2 domain. TTR-52 is proposed to bind PtdSer via an "ion-mediating" PtdSer-binding mode. Intensive functional studies show that CED-1 binds TTR-52 through its N-terminal EMI domain and that the hydrophobic region of the TTR-52 C terminus is involved in this interaction. In addition, unlike other PtdSer-binding domains, TTR-52 forms dimers, and its dimerization is important for its function in vivo. Our results reveal the first full-length structure of a bridging molecule and the mechanism underlying bridging molecule-mediated apoptotic cell recognition.