An allatotropin-like neuropeptide in Mesostoma ehrenbergii (Rhabdocoela, Platyhelminthes)

Abstract

Allatotropin (AT), a neuropeptide isolated on the basis of its ability to stimulate the synthesis of juvenile hormones (JHs) in insects, has also been found in other groups. In addition to this function, AT has proved to be myotropic. In the present study, we analyze its expression in the free-living turbellarian Mesostoma ehrenbergii (Platyhelminthes: Typhloplanida) and its probable functional relationship with the muscle tissue. The results show the presence of an AT-like peptide in neurons located in diVerent regions of the body of the Xatworm. The analysis of the presence of the peptide together with phalloidin labeling suggests a functional relationship between the peptide and the muscle tissue. This is particularly evident at the level of the pharynx, where the peptide induces contractions at concentrations of 10 ¡14 and 10 ¡12 M, suggesting that it is actually acting as a myoregulator. Detection of AT in several groups of protostomes but apparently not in deuterostomes suggests that this peptide could be a synapomorphic feature of protostomes. Indeed, the presence of AT in organisms that do not undergo metamorphosis could suggest that it was Wrst involved in myotropic activities, being the induction of the synthesis of JHs a secondary function.

Somatostatin signaling system as an ancestral mechanism: Myoregulatory activity of an Allatostatin-C peptide in Hydra

“…Neurosecretory cells exerting paracrine or yuxtracrine regulation appeared early in evolution, preceding the origin of neuronal and endocrine systems [2,32]. It has been proposed that neuropeptides showing both excitatory and inhibitory effects are the most ancient myoregulatory messengers, being present in Cnidaria, [15,24,[35][36][37]47].…”

“…The presence of AT-like peptides in both Cnidaria and Platyhelminthes, strongly suggests that the ancestral function of this peptide is related with muscle activity regulation, being the regulation of JH synthesis a synapomorphic feature of insects [2][3]12]. Allatostatins (ASTs) constitute a group of neuropeptides that has been originally characterized because of their inhibitory effect on the synthesis of JHs in insects.…”

Allatotropin: An Ancestral Myotropic Neuropeptide Involved in Feeding

“…The antibody recognizes A. aegypti AT with the following sequence of amino-acids: APFRNSEMMTARGF [28]. The specificity of antibody binding was previously demonstrated by preadsorption with the cognate peptide, both in insect species [36,37,52] as well as in other invertebrate groups [46,47]. Hydroids were then incubated with a FITC-labeled goat anti-rabbit secondary antibody (Santa Cruz Biotechnology) (1/1000 in blocking-buffer) for 24 h at 4°C.…”

“…In fact, genes codifying peptides sharing similarity with AT have been reported in the limpet Lottia gigantea (Gastropoda: Mollusca) and in the worms Capitella teleta (Polychaeta: Annelida) and Helobdella robusta (Hirudinea: Annelida) [44,45]. Recently, we have demonstrated the expression of an AT-like peptide in three species of free living flatworms (Platyhelminthes) from different groups of turbellaria (Catenulida, Macrostomorpha and Rhabdocoela), where the peptide is present in neurons morphologically and functionally associated with muscle tissues in the reproductive and digestive systems [46,47]. In fact, in the flatworm Mesostoma ehrenbergii (Rhabdocoela: Platyhelminthes), the exogenous administration of AT (10 -14 and 10 -12 M) induced muscular contractions, particularly in the pharynx, suggesting that it acts as a myoregulator [47].…”

“…Interestingly, the detection of AT in several groups of Protostomata but apparently not in Deuterostomata suggests that this peptide could be a synapomorphic feature of Protostomata. Indeed, the presence of AT in organisms that do not undergo metamorphosis suggests that it was originally involved in myotropic activities, the induction of the synthesis of JHs being a secondary function [47]. As a first approach to understand the evolutionary origin of this pleiotropic peptide, we decided to investigate the expression of AT-like peptides in Hydra plagiodesmica (Hydroazoa: Cnidaria).…”