Our work over the past few years has focussed particularly on the medically-important bug, Rhodnius prolixus. This bug takes enormous blood meals from humans, and during the subsequent excretion of excess salts and water (diuresis), the parasite, Trypanosoma cruzi, is transmitted to the human host where it causes Chagas disease. We are examining a variety of short term events which occur following the natural stimulus of a blood meal, including the neurohormonal control of diuresis, and also the cessation of diuresis. In particular, we are defining the precise input associated with feeding which results in elevations in haemolymph serotonin and diuretic peptide hormones (identified by us), describing the location and physiological properties of the neurosecretory cells which release these diuretic and anti-diuretic hormones, and their target sites (e.g. salivary glands, midgut, hindgut, Malpighian tubules, heart and epidermal cells). Blood gorging is also the stimulus for growth, development and reproduction, and so we are also studying these longer term events, and the involvement of similar families of neuropeptides.
Progress in this area has been facilitated and enhanced because of the Rhodnius genome project, and we have been successful in cloning, for the first time in Rhodnius, the genes for neuropeptides and GPCRs, synthesising the neuropeptides and examining their physiological effects.
This research also lays the foundation for pest control strategies, targeting neuropeptides as lead compounds. Since the parasite is transmitted during diuresis, one can argue that diuretic hormones actually control the transmission of Chagas disease. Interfering with this process should interfere with the transmission of Chagas disease. Our discovery of the diuretic and possibly more relevant antidiuretic hormones, is of some considerable importance.
Research Excellence Award: https://www.utm.utoronto.ca/vp-research/research-campus/researcher-profiles/biology/ian-orchard
Most Significant Contributions to Research; Students and Post-docs indicated in Bold. For more complete list see https://www.researchgate.net/profile/Ian_Orchard/contributions and https://loop.frontiersin.org/people/20992/overview
Orchard, I., Leyria, J., Lange, A.B. (2022) The hormonal and neural control of egg production in the historically important model insect, Rhodnius prolixus: A review, with new insights in this post-genomic era. Gen. Comp. Endocrinol. 321-322: 114030. https://doi.org/10.1016/j.ygcen.2022.114030
The R. prolixus genome is available and so the post-genomic era has arrived for this historic model insect. This review focuses on the female reproductive system and coordination over the production of eggs, emphasizing the classical (neuro)endocrinological studies that led to a model describing inputs from feeding and mating, and the neural control of egg-laying. We then review recent insights brought about by molecular analyses, including transcriptomics, that confirm, support, and considerably extends this model. We conclude this review with an updated model describing the events leading to full expression of egg production, and also provide a consideration of questions for future exploration and experimentation.
Al-Dailami, A.N., Leyria, J., Orchard, I. and Lange, A.B. (2022) Exploring the role of glycoprotein hormone GPA2/GPB5 in the medically important insect, Rhodnius prolixus. Peptides 149: 170710. https://doi.org/10.1016/j.peptides.2021.170710
In this study, we clone and characterize the transcripts for the glycoprotein hormone GPA2/GPB5 and its receptor (LGR1) in fifth instar Rhodnius prolixus, a hemimetabolous insect vector of Chagas disease. Sequence analyses reveals considerable identity and similarity between GPA2/GPB5 and LGR1 and those reported in other arthropod species. Using immunohistochemistry, we show that GPB5 is expressed throughout the CNS, and importantly is present in neurosecretory cells in the brain and abdominal neuromeres and their neurohemal organs, indicating a neurohormonal role for this signaling pathway. RNAinterference suggests that the GPA2/GPB5 signaling pathway may play roles during a prolonged unfed state and in feeding-related events.
Orchard, I., Leyria, J., Al-Dailami, A., Lange, A.B. (2021) Fluid secretion by Malpighian tubules of Rhodnius prolixus: Neuroendocrine control with new insights from a transcriptome analysis. Front Endocrinol (Lausanne). 2021; 12: 722487. doi: 10.3389/fendo.2021.722487
Rhodnius prolixus (the kissing bug and a major vector of Chagas disease) is an obligate blood feeder that in the case of the fifth instar consumes up to 10 times its unfed body weight in a single 20-minute feed. A post-prandial diuresis is initiated, within minutes of the start of gorging, in order to lower the mass and concentrate the nutrients of the meal. In R. prolixus, as with other insects, the Malpighian tubules play a critical role in diuresis. Malpighian tubules are not innervated, and their fine control comes under the influence of the neuroendocrine system that releases amines and neuropeptides as diuretic or antidiuretic hormones. These hormones act upon the Malpighian tubules via a variety of G protein-coupled receptors linked to second messenger systems that influence ion transporters and aquaporins; thereby regulating fluid secretion. This paper focuses on recent discoveries into the neuroendocrine control of the rapid post-prandial diuresis in R. prolixus, in order to emphasize new insights from a transcriptome analysis of Malpighian tubules taken from unfed and fed bugs.
Ayub, M., Lange, A.B., Orchard, I. (2021) Identification and characterization of the SIFamide receptor in the hemimetabolous Chagas disease vector, Rhodnius prolixus Stål, 1859, (Hemiptera, Reduviidae, Triatominae). Peptides, Volume 143, 170600.
In Rhodnius prolixus, we have previously shown the presence of SIFamidergic-like processes in neurohemal release sites and provided evidence for a role for Rhopr-SIFa in modulating heartbeat frequency and feeding behaviors. Here, the R. prolixus SIFamide receptor (RhoprSIFR) has been identified, cloned, and sequenced. Sequence analyses show high similarity and identity between the RhoprSIFR and other cloned SIFamide receptors. Quantitative PCR shows that the RhoprSIFR transcript is found in a variety of tissues, including those involved in feeding and reproduction. In unfed insects, high transcript expression is observed in the central nervous system and midgut, suggesting a role of Rhopr-SIFa in various processes related to feeding and digestion. Expression of the RhoprSIFR transcript changes between unfed, 24 h post-fed, and 7 d post-fed conditions. Expression of the RhoprSIFR transcript significantly increases in the anterior midgut and posterior midgut 7 d post-feeding and knockdown of the RhoprSIFR transcript significantly reduces the size of blood meal consumed. This data suggests a possible role for Rhopr-SIFa in regulating long-term post-feeding osmotic balance and digestion of the blood meal
Veenstra, J.A., Leyria, J., Orchard, I., Lange, A.B (2021) Identification of gonadulin and insulin-like growth factor from migratory locusts and their importance in reproduction in Locusta migratoria. Front. Endocrinol., 04 June 2021 | https://doi.org/10.3389/fendo.2021.693068
Many insect species have several genes coding for insulin-related peptides (IRPs), but so far only a single IRP gene has been identified in migratory locusts. Here, we report and characterize two other genes coding for peptides that are related to insulin, namely gonadulin and arthropod insulin-like growth factor (aIGF); peptides postulated to be orthologs of Drosophila melanogaster insulin-like peptides 8 and 6 respectively. In Locusta migratoria the aIGF transcript is expressed in multiple tissues as was previously reported for IRP in both L. migratoria and Schistocerca gregaria, but there are significant differences in expression patterns between the two species. The gonadulin transcript, however, seems specific to the ovary, whereas its putative receptor transcript is expressed most abundantly in the ovary, fat body and the central nervous system. Since the central nervous system-fat body-ovary axis is essential for successful reproduction, we studied the influence of gonadulin on vitellogenesis and oocyte growth. A reduction in the gonadulin transcript (via RNA interference) led to a significant reduction in vitellogenin mRNA levels in the fat body and a strong oocyte growth inhibition, thus suggesting an important role for gonadulin in reproduction in this species.