Figure 8

Model for the conserved action of Toll signals during Rhodnius dorso-ventral patterning. The hierarchical relationships between Toll and Bone Morphogenetic Protein pathways in dorso-ventral (DV) patterning have been established for Drosophila and Tribolium, either in terms of gene transcription or protein activity, and are displayed in simplified form to compare with relationships defined here for Rhodnius. Neither Tribolium nor Rhodnius Toll pathways regulate dpp expression, activity required to pattern the dorsal region of the Drosophila embryo. On the other hand, a feedback loop between Toll and dl is only present in Tribolium. In the three species analyzed, dl positively regulates sog expression. Arrows in black are those tested experimentally. Arrows in grey denote relations that are assumed based on conserved aspects and published evidence throughout the animal kingdom. Maternal, zygotic or maternal + zygotic expression are displayed in blue, red and pink, respectively. Maternal (blue) and zygotic (red) expression of dpp and sog are not gathered as one in Drosophila and Rhodnius since their epistatic relationships to the Toll pathway differ (Drosophila), or have not been fully analyzed (Rhodnius).