BackgroundCell-cell interactions are a basic principle for the organization of tissues and organs allowing them to perform integrated functions and to organize themselves spatially and temporally. Peptidic molecules secreted by neurons and epithelial cells play fundamental roles in cell-cell interactions, acting as local neuromodulators, neurohormones, as well as endocrine and paracrine messengers. Allatotropin (AT) is a neuropeptide originally described as a regulator of Juvenile Hormone synthesis, which plays multiple neural, endocrine and myoactive roles in insects and other organisms.MethodsA combination of immunohistochemistry using AT-antibodies and AT-Qdot nanocrystal conjugates was used to identify immunoreactive nerve cells containing the peptide and epithelial-muscular cells targeted by AT in Hydra plagiodesmica. Physiological assays using AT and AT- antibodies revealed that while AT stimulated the extrusion of the hypostome in a dose-response fashion in starved hydroids, the activity of hypostome in hydroids challenged with food was blocked by treatments with different doses of AT-antibodies.ConclusionsAT antibodies immunolabeled nerve cells in the stalk, pedal disc, tentacles and hypostome. AT-Qdot conjugates recognized epithelial-muscular cell in the same tissues, suggesting the existence of anatomical and functional relationships between these two cell populations. Physiological assays indicated that the AT-like peptide is facilitating food ingestion.SignificanceImmunochemical, physiological and bioinformatics evidence advocates that AT is an ancestral neuropeptide involved in myoregulatory activities associated with meal ingestion and digestion.

No abstract

Juvenile hormones (JHs) are sesquiterpenoids synthesized by the corpora allata (CA). They play critical roles during insect development and reproduction. The first JH was described in 1934 as a "metamorphosis inhibitory hormone" in Rhodnius prolixus by Sir Vincent B. Wigglesworth. Remarkably, in spite of the importance of R. prolixus as vectors of Chagas disease and model organisms in insect physiology, the original JH that Wigglesworth described for the kissing-bug R. prolixus remained unidentified. We employed liquid chromatography mass spectrometry to search for the JH homologs present in the hemolymph of fourth instar nymphs of R. prolixus. Wigglesworth's original JH is the JH III skipped bisepoxide (JHSB3), a homolog identified in other heteropteran species. Changes in the titer of JHSB3 were studied during the 10-day long molting cycle of 4 th instar nymph, between a blood meal and the ecdysis to 5 th instar. In addition we measured the changes of mRNA levels in the CA for the 13 enzymes of the JH biosynthetic pathway during the molting cycle of 4 th instar. Almost 90 years after the first descriptions of the role of JH in insects, this study finally reveals that the specific JH homolog responsible for Wigglesworth's original observations is JHSB3.Sir Vincent B. Wigglesworth, the famous British insect endocrinologist, published a series of three classical manuscripts in the years 1934, 1936 and 1940 that described the existence of an "inhibitory hormone" that prevented metamorphosis in the early nymphal stages of the blood-sucking bug Rhodnius prolixus 1-3 . The manuscripts contained a series of elegant studies, including a parabiosis techniques that allowed the mixing of the hemolymph of fourth and fifth instar nymphs, as well as corpora allata (CA) transplantation experiments. These studies permitted Wigglesworth to demonstrate for the first time the existence of an "inhibitory hormone" secreted by the CA and delivered to target tissues by the hemolymph. In his latest article, Wigglesworth proposed for the first time to name the "inhibitory hormone" as "juvenile hormone" (JH) 3 . Wigglesworth also used transplantation and parabiosis experiments to reveal that the CA of the 4 th instar nymphs of R. prolixus was an equally good source of a "yolk-forming hormone", whereas the CA of a 5 th instar nymph was ineffective. He concluded that only a single hormone, the "Juvenile Hormone", was responsible for both actions, the inhibition of metamorphosis, as well as the control of development of the reproductive organs in the adult 4 .After the pioneering studies by Wigglesworth and others, the chemical nature of JH remained unidentified until the late 1960's. The first two JHs, named JH I and II, were isolated from the moth Hyalophora cecropia. They were identified as sesquiterpenes, with a methyl ester (α, β-unsaturated) at the C1 position and an epoxide ring at the C10-C11 position 5,6 . Juvenile hormone III, the homolog found in most insects, was described in 1973 from the moth Manduca sexta 7 . Finally, two dou...