Mollayeva Shirin, Orchard Ian, Lange Angela B
Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6, Canada.
Gen Comp Endocrinol. 2018 Mar 1;258:79-90. doi: 10.1016/j.ygcen.2017.07.005. Epub 2017 Jul 8.
Rhodnius prolixus is a blood-gorging insect and a vector for human Chagas disease. The insect transmits the disease following feeding, when it excretes urine and feces contaminated with the Trypanosoma cruzi parasite. A corticotropin-releasing factor-like peptide acts as a diuretic hormone in R. prolixus (Rhopr-CRF/DH); however, its distribution throughout the insect's central nervous system (CNS) and the expression of its receptor in feeding-related tissue as well as the female reproductive system suggests a multifaceted role for the hormone beyond that of diuresis. Here we investigate the involvement of Rhopr-CRF/DH in feeding and reproduction in R. prolixus. Immunohistochemistry of the CNS showed diminished CRF-like staining in neurosecretory cells (NSCs) of the mesothoracic ganglionic mass (MTGM) immediately following feeding, and partial restocking of those same cells two hours later, indicating Rhopr-CRF/DH stores in this regions are involved in feeding. The results of the temporal qPCR analysis were consistent with the immunohistochemical findings, showing an increase in Rhopr-CRF/DH transcript expression in the MTGM immediately after feeding, presumably capturing the restocking of Rhopr-CRF/DH in the lateral NSCs following release of the peptide during feeding. Elevating haemolymph Rhopr-CRF/DH titres by injection of Rhopr-CRF/DH prior to feeding resulted in the intake of a significantly smaller blood meal in 5th instars and adults without an apparent effect on the rate of short-term diuresis. When adult females were injected with Rhopr-CRF/DH, they also produced and laid significantly fewer eggs. Finally, in vitro oviduct contraction assays illustrate that Rhopr-CRF/DH inhibits the amplitude of contractions of the lateral oviducts, highlighting a potential mechanism via which the hormone diminishes reproductive capacity. To conclude, the study of the Rhopr-CRF/DH pathway, its components and mechanisms of action, has implications for vector control by highlighting targets to alter feeding, diuresis, and reproduction of this disease vector.
长红猎蝽是一种吸食血液的昆虫，也是人类恰加斯病的传播媒介。这种昆虫在进食后会排出被克氏锥虫寄生虫污染的尿液和粪便，从而传播疾病。一种促肾上腺皮质激素释放因子样肽在长红猎蝽中充当利尿激素（Rhopr-CRF/DH）；然而，它在昆虫中枢神经系统（CNS）中的分布以及其受体在与进食相关组织和雌性生殖系统中的表达表明，该激素的作用不止于利尿，具有多方面的作用。在此，我们研究Rhopr-CRF/DH在长红猎蝽进食和繁殖中的作用。中枢神经系统的免疫组织化学显示，进食后中胸神经节团（MTGM）的神经分泌细胞（NSCs）中CRF样染色减少，两小时后这些细胞部分重新储备，表明该区域的Rhopr-CRF/DH储备与进食有关。实时定量PCR分析结果与免疫组织化学结果一致，显示进食后MTGM中Rhopr-CRF/DH转录本表达增加，推测是在进食期间肽释放后，外侧NSCs中Rhopr-CRF/DH重新储备的体现。在进食前注射Rhopr-CRF/DH以提高血淋巴中Rhopr-CRF/DH滴度，导致五龄若虫和成虫摄入的血餐量显著减少，而对短期利尿速率没有明显影响。当成年雌性注射Rhopr-CRF/DH时，它们产卵的数量也显著减少。最后，体外输卵管收缩试验表明，Rhopr-CRF/DH抑制外侧输卵管的收缩幅度，突出了该激素降低生殖能力的潜在机制。总之，对Rhopr-CRF/DH途径及其组成部分和作用机制的研究，通过突出改变这种疾病媒介的进食、利尿和繁殖的靶点，对病媒控制具有重要意义。
