Biology subjects

Bauknecht, P.

Publications and source records attributed to Bauknecht, P..

5 recordsLinked to original sources

bioRxiv2019

A G-protein-coupled receptor mediates neuropeptide-induced oocyte maturation in the jellyfish Clytia

The reproductive hormones that trigger oocyte meiotic maturation and release from the ovary vary greatly between animal species. Identification of receptors for these Maturation Inducing Hormones (MIHs), and understanding how they initiate the largely conserved maturation process, remain important challenges. In hydrozoan cnidarians including the jellyfish Clytia hemisphaerica, MIH comprises neuropeptides released from somatic cells of the gonad. We identified the receptor (MIHR) for these MIH neuropeptides in Clytia using cell culture-based \"deorphanization\" of candidate oocyte-expressed GPCRs. MIHR mutant jellyfish generated using CRISPR-Cas9 had severe defects in gamete development or in spawning both in males and females. Female gonads, or oocytes isolated from MIHR mutants, failed to respond to synthetic MIH. Treatment with the cAMP analogue 5Br-cAMP to mimic cAMP rise at maturation onset rescued meiotic maturation and spawning. Injection of inhibitory antibodies to GS into wild type oocytes phenocopied the MIHR mutants. These results provide the molecular links between MIH stimulation and meiosis initiation in hydrozoan oocytes. Molecular phylogeny grouped Clytia MIHR with a subset of bilaterian neuropeptide receptors including Neuropeptide Y, Gonadotropin Inhibitory Hormone, pyroglutamylated RFamide and Luqin, all upstream regulators of sexual reproduction. This identification and functional characterisation of a cnidarian peptide GPCR advances our understanding of oocyte maturation initiation and sheds light on the evolution of neuropeptide-hormone systems.

developmental biology↗

bioRxiv2019

A nemertean excitatory peptide/CCHamide regulates ciliary swimming in the larvae of Lineus longissimus

BackgroundThe trochozoan excitatory peptide (EP) and its ortholog, the arthropod CCHamide, are neuropeptides that are only investigated in very few animal species. Previous studies on different trochozoan species focused on their physiological effect in adult specimens, demonstrating a myo-excitatory effect, often on tissues of the digestive system. The function of EP in the planktonic larvae of trochozoans has not yet been studied.\n\nResultsWe surveyed transcriptomes from species of various spiralian (Orthonectia, Nemertea, Brachiopoda, Entoprocta, Rotifera) and ecdysozoan taxa (Tardigrada, Onychophora, Priapulida, Loricifera, Nematomorpha) to investigate the evolution of EPs/CCHamides in protostomes. We found that the EPs of several pilidiophoran nemerteans show a characteristic difference in their C-terminus. Deorphanization of a pilidiophoran EP receptor showed, that the two isoforms of the nemertean Lineus longissimus EP activate a single receptor. We investigated the expression of EP in L. longissimus larvae and juveniles with customized antibodies and found that EP-positive nerves in larvae project from the apical organ to the ciliary band and that EP is expressed more broadly in juveniles in the neuropil and the prominent longitudinal nerve cords. While exposing juvenile L. longissimus specimens to synthetic excitatory peptides did not show any obvious effect, exposure of larvae to either of the two EPs increased the beat frequency of their locomotory cilia and shifted their vertical swimming distribution in a water column upwards.\n\nConclusionOur results show that EP/CCHamide peptides are broadly conserved in protostomes. We show that the EP increases the ciliary beat frequency of L. longissimus larvae, which shifts their vertical distribution in a water column upwards. Endogenous EP may be released at the ciliary band from the projections of apical organ EP-positive neurons to regulate ciliary beating. A locomotory function of EP in L. longissimus larvae, compared to the association of EP/CCHamides with the digestive system in other animals suggests a dynamic integration of orthologous neuropeptides into different functions during evolution.

neuroscience↗

bioRxiv2018

Dual signaling of Wamide myoinhibitory peptides through a peptide-gated channel and a GPCR in Platynereis

Neuropeptides commonly signal by metabotropic G-protein coupled receptors (GPCRs). In some mollusks and cnidarians, RFamide neuropeptides mediate fast ionotropic signaling by peptide-gated ion channels that belong to the DEG/ENaC family. Here we describe a neuropeptide system with a dual mode of signaling by both a peptide-gated channel and a GPCR. We identified and characterised a peptide-gated channel in the marine annelid Platynereis dumerilii that is specifically activated by Wamide myoinhibitory peptides derived from the same proneuropeptide. The myoinhibitory peptide-gated ion channel (MGIC) belongs to the DEG/ENaC family and is paralogous to RFamide-gated channels. Platynereis myoinhibitory peptides also activate a previously described GPCR, MAG. We measured the potency of all Wamides on both MGIC and MAG and identified peptides that preferentially activate one or the other receptor. Analysis of a single-cell transcriptome resource indicates that MGIC and MAG signal to distinct target neurons. The identification of a Wamide-gated channel suggests that peptide-gated channels are more diverse and widespread in animals than previously appreciated. The possibility of neuropeptide signaling by both ionotropic and metabotropic receptors to different target cells in the same organism highlights an additional level of complexity in peptidergic signaling networks.

neuroscience↗

bioRxiv2017

An ancient FMRFamide-related peptide-receptor pair induces defense behavior in a brachiopod larva

Animals show different behaviors that can consist of various spatially or temporally separated sub-reactions. Even less complex organisms, like ciliated larvae that display important behaviors (e.g. metamorphosis, defense, feeding), need to coordinate coherent sub-reactions with their simple nervous system. These behaviors can be triggered by neuropeptides, which are short signaling peptides. Despite the high diversity of neuropeptides in animals, and although their immunoreactivity is widely used in morphological studies of animal nervous systems (e.g. FMRFamide), their function and role in trochozoan larval behavior has so far only been tested in a few cases. When mechanically disturbed, the planktonic larvae of the brachiopod Terebratalia transversa protrude their stiff and pointy chaetae in a defensive manner and sink down slowly: a startle reaction that is known from different chaetous trochozoan larvae. We found that both of these reactions can be induced simultaneously by the FMRFamide-related neuropeptide FLRFamide. We deorphanized the Terebratalia FLRFamide receptor and found its expression spatially separated in the apical lobe at the prototroch of the larvae and in the trunk musculature, which correlates with the tissues that are responsible to perform the two sub-reactions. A behavioral assay showed a decreasing efficiency of modified peptides in triggering this behavior, which correlates with the decreasing efficiency of activating the FLRFamide receptor in transfected CHO-K1 cells. Immunohistochemistry and in situ hybridization show FLRFamidergic neurons in the apical lobe as well as next to the trunk musculature. Our results show that the single neuropeptide FLRFamide can specifically induce the two coherent sub-reactions of the T. transversa startle behavior.

neuroscience↗

bioRxiv2017

Synaptic and peptidergic connectome of a neurosecretory centre in the annelid brain

Neurosecretory centres in animal brains use peptidergic signalling to influence physiology and behaviour. Understanding neurosecretory centre function requires mapping cell types, synapses, and peptidergic networks. Here we use electron microscopy and gene expression mapping to analyse the synaptic and peptidergic connectome of an entire neurosecretory centre. We mapped 78 neurosecretory neurons in the brain of larval Platynereis dumerilii, a marine annelid. These neurons form an anterior neurosecretory organ expressing many neuropeptides, including hypothalamic peptide orthologues and their receptors. Analysis of peptide-receptor pairs revealed sparsely connected networks linking specific neuronal subsets. We experimentally analysed one peptide-receptor pair and found that a neuropeptide can couple neurosecretory and synaptic brain signalling. Our study uncovered extensive non-synaptic signalling within a neurosecretory centre and its connection to the synaptic brain.

neuroscience↗