Allatotropin: an ancestral myotropic neuropeptide involved in feeding.

BACKGROUND: Cell-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. METHODS: A 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. CONCLUSIONS: AT 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. SIGNIFICANCE: Immunochemical, physiological and bioinformatics evidence advocates that AT is an ancestral neuropeptide involved in myoregulatory activities associated with meal ingestion and digestion.

Expression of a neuropeptide similar to allatotropin in free living turbellaria (platyhelminthes).

Mechanisms coordinating cell-cell interaction have appeared early in evolution. Allatotropin (AT), a neuropeptide isolated based on its ability to stimulate the synthesis of juvenile hormones (JHs) in insects has also been found in other invertebrate phyla. Despite this function, AT has proved to be myotropic. In the present study we analyze its expression in two groups of Turbellaria (Catenulida, Macrostomida), and its probable relationship with muscle tissue. The results show the presence of an AT-like peptide in the free living turbellaria analyzed. The analysis of the expression of the peptide together with phalloidin, suggests a functional relationship between the peptide and muscle tissue, showing that it could be acting as a myoregulator. The finding of immunoreactive fibers associated with sensory organs like ciliated pits in Catenulida and eyes in Macrostomida makes probable that AT could play a role in the physiological mechanisms controlling circadian activities. Furthermore, the existence of AT in several phyla of Protostomata suggests that this peptide could be a synapomorphic feature of this group. Indeed, the presence in organisms that do not undergo metamorphosis, could be signaling that it was first involved in myotropic activities, being the stimulation of the synthesis of JHs a secondary function acquired by the phylum Arthropoda.