Formation of the Drosophila embryonic termini is controlled by the localized activation of the receptor tyrosine kinase Torso. Both Torso and Torso's presumed ligand, Trunk, are expressed uniformly in the early embryo. Polar activation of Torso requires Torso-like, which is expressed by follicle cells adjacent to the ends of the developing oocyte. We find that Torso expressed at high levels in cultured Drosophila cells is activated by individual application of Trunk, Torso-like or another known Torso ligand, Prothoracicotropic Hormone. In addition to assays of downstream signaling activity, Torso dimerization was detected using bimolecular fluorescence complementation. Trunk and Torso-like were active when co-transfected with Torso and when presented to Torso-expressing cells in conditioned medium. Trunk and Torso-like were also taken up from conditioned medium specifically by cells expressing Torso. At low levels of Torso, similar to those present in the embryo, Trunk and Torso-like alone were ineffective but acted synergistically to stimulate Torso signaling. Our results suggest that Torso interacts with both Trunk and Torso-like, which cooperate to mediate dimerization and activation of Torso at the ends of the Drosophila embryo.
The authors declare no competing or financial interests.
S.A., L.M.S. and D.S.S. initiated the study, designed the experiments and interpreted their results and wrote the manuscript. S.A. performed the experiments. D.S.S. contributed to the generation of DNA constructs used in these studies.
This work was supported by the March of Dimes Foundation (1-FY13-403 to D.S.S.) and the National Institutes of Health (RO1 GM077337 to D.S.S.). The Drosophila Genomics Resource Center is supported by the National Institutes of Health (2P40OD010949-10A1). Deposited in PMC for release after 12 months.
Supplementary information available online at http://dev.biologists.org/lookup/doi/10.1242/dev.146076.supplemental
- Received October 26, 2016.
- Accepted December 30, 2016.