The comprehensive analysis of DEG/ENaC subunits in Hydrareveals a large variety of peptide-gated channels, potentially involved in neuromuscular transmission

Abstract

BackgroundIt is generally the case that fast transmission at neural synapses is mediated by small molecule neurotransmitters. The simple nervous system of the cnidarian Hydra, however, contains a large repertoire of neuropeptides and it has been suggested that neuropeptides are the principal transmitters of Hydra. An ion channel directly gated by Hydra-RFamide neuropeptides has indeed been identified in Hydra – the Hydra Na+ channel (HyNaC) 2/3/5, which is expressed at the oral side of the tentacle base. Hydra-RFamides are more widely expressed, however, being found in neurons of the head and peduncle region. Here, we explore whether further peptide-gated HyNaCs exist, where in the animal they are expressed, and whether they are all gated by Hydra-RFamides.ResultsWe report molecular cloning of seven new HyNaC subunits – HyNaC6 to HyNaC12, all of which are members of the DEG/ENaC gene family. In Xenopus oocytes, these subunits assemble together with the four already known subunits into thirteen different ion channels that are directly gated by Hydra-RFamide neuropeptides with high affinity (up to 40 nM). In situ hybridization suggests that HyNaCs are expressed in epitheliomuscular cells at the oral and the aboral side of the tentacle base and at the peduncle. Moreover, diminazene, an inhibitor of HyNaCs, delayed tentacle movement in live Hydra.ConclusionsOur results show that Hydra has a large variety of peptide-gated ion channels that are activated by a restricted number of related neuropeptides. The existence and expression pattern of these channels, and behavioral effects induced by channel blockers, suggests that Hydra co-opted neuropeptides for fast neuromuscular transmission.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-014-0084-2) contains supplementary material, which is available to authorized users.

Peptide-gated ion channels and the simple nervous system of Hydra

“…In a recent report (Assmann et al, 2014), the seven additional DEG/ENaC subunits from Hydra magnipapillata shown in Fig. 10 have been functionally characterized and the results support their role in neuromuscular transmission.…”

Functional and pharmacological characterization of two different ASIC1a/2a heteromers reveals their sensitivity to the spider toxin PcTx1

“…Electrophysiological measurements were conducted as previously described3042 by expression of ASICs in stage V and VI oocytes of Xenopus laevis . Oocytes were surgically removed under anaesthesia (4 g l −1 tricaine methanesulfonate for 20–30 min) from adult Xenopus laevis females.…”

New techniques, applications and perspectives in neuropeptide research

“…In contrast to FaNaC, HyNaC is an unselective cation channel with a high Ca 2+ permeability (Dürrnagel et al, 2012) (Table 2). Soon after, all 12 DEG/ENaCs of Hydra were cloned, and it was shown that Hydra likely contains at least six different functional HyNaCs (Assmann et al, 2014). All are heterotrimers consisting of three different subunits activated by Hydra-RFamides I and II, and all are unselective cation channels (Assmann et al, 2014) (Table 2).…”

“…Soon after, all 12 DEG/ENaCs of Hydra were cloned, and it was shown that Hydra likely contains at least six different functional HyNaCs (Assmann et al, 2014). All are heterotrimers consisting of three different subunits activated by Hydra-RFamides I and II, and all are unselective cation channels (Assmann et al, 2014) (Table 2). It is not clear why Hydra evolved such a variety of peptide-gated channels with similar properties, but differential targeting and ligand affinity are two possibilities.…”