Abstract
BackgroundInsect embryonic dorso-ventral patterning depends greatly on two pathways: the Toll pathway and the Bone Morphogenetic Protein pathway. While the relative contribution of each pathway has been investigated in holometabolous insects, their role has not been explored in insects with a hemimetabolous type of development. The hemimetabolous insect Rhodnius prolixus, an important vector of Chagas disease in the Americas, develops from an intermediate germ band and displays complex movements during katatrepsis that are not observed in other orders. However, little is known about the molecular events that regulate its embryogenesis. Here we investigate the expression and function of genes potentially involved in the initial patterning events that establish the embryonic dorso-ventral axis in this hemipteran.ResultsWe establish a staging system for early embryogenesis that allows us to correlate embryo morphology with gene expression profiles. Using this system, we investigate the role of Toll pathway genes during embryogenesis. Detailed analyses of gene expression throughout development, coupled with functional analyses using parental RNA interference, revealed that maternal Toll is required to establish germ layers along the dorso-ventral axis and for embryo placement along the anterior-posterior axis. Interestingly, knockdown of the Toll pathway effector Rp-dorsal appears to regulate the expression of the Bone Morphogenetic Protein antagonist Rp-short-gastrulation.ConclusionsOur results indicate that Toll signals are the initiating event in dorso-ventral patterning during Rhodnius embryogenesis, and this is the first report of a conserved role for Toll in a hemipteran. Furthermore, as Rp-dorsal RNA interference generates anteriorly misplaced embryos, our results indicate a novel role for Toll signals in establishment of the anterior-posterior axis in Rhodnius.Electronic supplementary materialThe online version of this article (doi:10.1186/2041-9139-5-38) contains supplementary material, which is available to authorized users.
Highlights
Insect embryonic dorso-ventral patterning depends greatly on two pathways: the Toll pathway and the Bone Morphogenetic Protein pathway
Establishing a staging system to study Rhodnius prolixus early embryonic development The hemiptera R. prolixus develops from an intermediate germ band, where the anlagen of the head and thoracic segments are established before gastrulation, while the abdominal segments are generated by a secondary process from a posterior growth zone
Staining in oocytes probably originated from the nurse cells through trophic cords. This staining is specific as it was lost in Rhodnius prolixus (Rp)-Toll knockdowns (Additional file 3). Since it is a putative effector of the Toll pathway, we investigated the expression of Rp-dl during oogenesis and embryogenesis (Figure 3C)
Summary
Insect embryonic dorso-ventral patterning depends greatly on two pathways: the Toll pathway and the Bone Morphogenetic Protein pathway. We investigate the expression and function of genes potentially involved in the initial patterning events that establish the embryonic dorso-ventral axis in this hemipteran. Two major pathways have been described that pattern the DV axis in arthropods: the Toll receptor pathway and the Bone Morphogenetic Protein (BMP) pathway. Their respective contribution to DV patterning, as well as their maternal versus zygotic functions, varies among species (see references in [2]). BMPs play a key role in setting up the DV axis in Tribolium, and Tc-Toll does not regulate Tc-dpp expression [5,7]
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