Biology subjects

Jekely, G.

Publications and source records attributed to Jekely, G..

At least 19 recordsLinked to original sources

bioRxiv2026

From promiscuity to specialization: The origin of cholinergic and monoaminergic signaling is pre-bilaterian

The emergence of chemical neurotransmission was key to the evolution of nervous systems, yet when the different transmitter systems arose remains unclear. Biogenic amines (here, acetylcholine and the monoamines) have been reported in non-bilaterian animals and even outside Metazoa, but their physiological role has only recently begun to be resolved, and phylogenetic surveys of the bilaterian machinery have restricted dedicated monoaminergic signaling to Bilateria. Combining targeted metabolomics, molecular phylogenies, structural modeling and binding-affinity prediction, single-cell expression analysis and immunochemistry, we show that cholinergic and monoaminergic signaling predate Bilateria. We detect acetylcholine, dopamine, histamine, adrenaline, tyramine, 2-phenylethylamine and tryptamine in a sponge and two cnidarians, and identify broad-specificity enzymes and transporters able to produce and load them. These genes are co-expressed in both neuronal and non-neuronal cell types, indicating that amine signaling was never confined to the nervous system. Two Hydra vulgaris muscarinic receptor orthologs retain a fully conserved orthosteric site and are predicted to bind acetylcholine as strongly as their bilaterian counterparts, and muscle-type nicotinic receptor subunits are co-expressed with Rapsyn-related genes in cnidarian muscle cells, placing cholinergic neuromuscular signaling in the cnidarian-bilaterian ancestor. Specialization came later in Bilateria, where gene duplications produced substrate-specific enzymes (ChAT, TH, TPH), dedicated vesicular transporters (VAChT, VMAT) and ligand-selective receptors. Biogenic amine signaling is thus not a bilaterian innovation but an ancient mode of cellular communication that evolved from generalist to specialist machinery.

evolutionary biology↗

bioRxiv2026

Sample preparation optimisation for array tomography volume EM of entire organisms: a case study for marine larvae

Serial-sectioning electron microscopy allows the exploration of the 3D ultrastructure of cells, tissues or whole organisms. Sample preparation is a critical step for this technique, which determines the quality of downstream imaging and analysis. Here we optimize a high-pressure freezing sample-preparation workflow for larvae of the marine annelid Platynereis dumerilii. We tested several fixation and staining methods and screened a large number of specimens by synchrotron X-ray imaging to evaluate specimen integrity and contrast. We further evaluated selected blocks by array tomography SEM to select the best performing protocols. Our protocols and robust workflow could be adapted to similar marine planktonic organisms including ciliated invertebrate larvae.

developmental biology↗

bioRxiv2025

Neural Connectome of the Ctenophore Statocyst

Ctenophores possess a unique gravity receptor (statocyst) in their aboral organ formed by four clusters of ciliated balancer cells that collectively support a statolith. During reorientation, differential loads on the balancer cilia lead to altered beating of the ciliated comb rows to elicit turns. To study the neural bases of gravity sensing, we used volume electron microscopy (vEM) to image the aboral organ of the ctenophore Mnemiopsis leidyi. We reconstructed 1011 cells, including syncytial neurons that form a nerve net. The syncytial neurons synapse on the balancer cells and also form reciprocal connections with the bridge cells that span the statocyst. High-speed imaging revealed that balancer cilia beat and arrest in a coordinated manner but with differences between the sagittal and tentacular planes of the animal, reflecting nerve-net organisation. Our results suggest a coordinating rather than sensory-motor function for the nerve net and inform our understanding of the diversity of nervous-system organisation across animals.

animal behavior and cognition↗

bioRxiv2025

Functional and phylogenetic analysis of placozoan GPCRs reveal the prebilaterian origin of monoaminergic signalling.

Monoamines are biologically active compounds crucial for neurotransmission and various physiological processes. They include neurotransmitters like serotonin, dopamine, and melatonin, which regulate mood, movement, and sleep in humans. In ecdysozoans, monoamines such as tyramine are important for modulating locomotion, learning, and feeding. The monoaminergic signalling system has been considered a bilaterian innovation, with conflicting evidence supporting its existence in earlier branching, non-bilaterian animals. Here, we challenge the bilaterian origin hypothesis by combining large-scale receptor deorphanisation with phylogenetic analyses to identify monoamine receptors from the placozoan Trichoplax adhaerens. We demonstrate that these receptors are homologous to known bilaterian GPCRs, and behavioural assays demonstrate that monoamines like tyramine and tryptamine affect the speed of locomotion and body shape of this animal, respectively. These responses, together with the presence of biosynthetic enzymes for these molecules, reveal that monoaminergic signalling is both active and endogenous in placozoans. Our findings provide compelling evidence for a prebilaterian origin of monoaminergic systems, reshaping our understanding of early nervous system evolution.

evolutionary biology↗

bioRxiv2025

Dynamics and emergence of metachronal waves in the ciliary band of a metazoan larva

Both natural and synthetic ciliary arrays exhibit diverse coordination patterns. Proper coordination of cilia is essential for the normal physiology of many organisms, from single cells to humans. Yet despite decades of research the mechanisms of cilia coordination remains disputed, particularly the question of how coordinated waves of activity known as metachronal waves arise in different ciliated systems. In many aquatic larvae that rely on ciliary motility to swim, the cilia are often arranged ornately in arrays or bands, within which robust metachronal waves propagate. Here, to resolve the origins of ciliary metachronism, we target the equatorial ciliary band of the marine annelid, Platynereis dumerelii, using whole-body high-speed imaging, and physical and biological manipulations. The results reveal an unprecedented wave structure featuring strong coupling within individual multiciliated cells that breaks down across cell boundaries, and absence of global coupling across the organism. Using laser ablation to create gaps in the ciliary band, we quantify the resulting disruption to wave propagation, revealing the extent of interciliary phase-locking and implicating steric interactions as an important contributor to coordination. The larvae also exhibit spontaneous whole-body ciliary arrests which allow us to study wave emergence and re-establishment for the first time, revealing a novel role of the animals nervous system in the dynamic coupling of cilia.

biophysics↗

bioRxiv2025

A scotophobic response characterised by body contraction and ciliary arrest in Acropora coral larvae

Planulae of the reef-building coral Acropora millepora exhibit whole-body contraction and ciliary arrest after exposure to sudden light dimming. Quantitative behavioural assays confirmed reductions in swimming speed and alterations in vertical and horizontal movement under alternating light and dark conditions. High-speed microscopy revealed that ciliary activity ceases upon dimming, while the typically elongated body contracts into a rounded form, altering swimming behaviour. These larval responses suggest an adaptive mechanism to regulate positioning within the highly structured and complex light environment of reef habitats, critical for coral recruitment and survival.

neuroscience↗

bioRxiv2024

Whole-body connectome of a segmented annelid larva

Nervous systems coordinate effectors across the body during movements. We know little about the cellular-level structure of synaptic circuits for such body-wide control. Here we describe the whole-body synaptic connectome of a segmented larva of the marine annelid Platynereis dumerilii. We reconstructed and annotated over 9,000 neuronal and non-neuronal cells in a whole-body serial electron microscopy dataset. Differentiated cells were classified into 202 neuronal and 92 non-neuronal cell types. We analyse modularity, multisensory integration, left-right and intersegmental connectivity and motor circuits for ciliated cells, glands, pigment cells and muscles. We identify several segment-specific cell types, demonstrating the heteromery of the annelid larval trunk. At the same time, segmentally repeated cell types across the head, the trunk segments and the pygidium suggest the serial homology of all segmental body regions. We also report descending and ascending pathways, peptidergic circuits and a multi-modal mechanosensory girdle. Our work provides the basis for understanding whole-body coordination in an entire segmented animal.

neuroscience↗

bioRxiv2024

Microalgal biofilm induces larval settlement in the model marine worm Platynereis dumerilii

A free-swimming larval stage features in many marine invertebrate life cycles. To transition to a seafloor-dwelling juvenile stage, larvae need to settle out of the plankton, guided by specific environmental cues that lead them to an ideal habitat for their future life on the seafloor. Although the marine annelid Platynereis dumerilii has been cultured in research labs since the 1950s and has a free-swimming larval stage, specific environmental cues that induce settlement in this nereid worm are yet to be identified. Here we demonstrate that microalgal biofilm is a key settlement cue for P. dumerilii larvae, inducing earlier onset of settlement, and enhancing subsequent juvenile growth as a primary food source. We tested the settlement response of P. dumerilii to 40 different strains of microalgae, predominantly diatom species, finding that P. dumerilii have species-specific preferences in their choice of settlement substrate. The most effective diatom species for inducing P. dumerilii larval settlement were benthic pennate species including Grammatophora marina, Achnanthes brevipes, and Nitzschia ovalis. The identification of specific environmental cues for P. dumerilii settlement enables a link between its ecology and the sensory and nervous system signalling that regulate larval behaviour and development. Incorporation of diatoms into P. dumerilii culture practices will improve the husbandry of this marine invertebrate model.

zoology↗

bioRxiv2023

The development of the adult nervous system in the annelid Owenia fusiformis

BackgroundThe evolutionary origins of animal nervous systems remain contentious because we still have a limited understanding of neural development in most major animal clades. Annelids -- a species-rich group with centralised nervous systems -- have played central roles in hypotheses about the origins of animal nervous systems. However, most studies have focused on adults of deeply nested species in the annelid tree. Recently, Owenia fusiformis has emerged as an informative species to reconstruct ancestral traits in Annelida, given its phylogenetic position within the sister clade to all remaining annelids. MethodsCombining immunohistochemistry of the conserved neuropeptides FVamide-lir, RYamide-lir, RGWamide-lir and MIP-lir with gene expression, we comprehensively characterise neural development from larva to adulthood in Owenia fusiformis. ResultsThe early larval nervous system comprises a neuropeptide-rich apical organ connected through peripheral nerves to a prototroch ring and the chaetal sac. There are seven sensory neurons in the prototroch. A bilobed brain forms below the apical organ and connects to the ventral nerve cord of the developing juvenile. During metamorphosis, the brain compresses, becoming ring-shaped, and the trunk nervous system develops several longitudinal cords and segmented lateral nerves. ConclusionsOur findings reveal the formation and reorganisation of the nervous system during the life cycle of O. fusiformis, an early-branching annelid. Despite its apparent neuroanatomical simplicity, this species has a diverse peptidergic nervous system, exhibiting morphological similarities with other annelids, particularly at the larval stages. Our work supports the importance of neuropeptides in animal nervous systems and the evolution of biphasic life cycles.

developmental biology↗

bioRxiv2023

Nitric oxide feedback to ciliary photoreceptor cells gates a UV avoidance circuit

Nitric oxide (NO) produced by nitric-oxide synthase (NOS) is a key regulator of animal physiology. Here we uncover a function for NO in the integration of UV exposure and the gating of a UV-avoidance circuit. We studied UV/violet avoidance mediated by brain ciliary photoreceptors (cPRCs) in larvae of the annelid Platynereis dumerilii. In the larva, NOS is expressed in interneurons (INNOS) postsynaptic to cPRCs. UV stimulation of cPRCs triggers INNOS activation and NO production. NO signals retrogradely to cPRCs to induce their sustained post-stimulus activation through an unconventional guanylate cyclase. This late activation drives ciliary beating through serotonergic ciliomotor neurons during UV avoidance. In NOS mutants, retrograde signalling, ciliary activation and UV avoidance are defective. By mathematical modelling, we recapitulate phototransduction and circuit dynamics in wild-type and mutant larvae. Our results reveal how NO-mediated retrograde signalling gates a synaptic circuit and induces short-term memory of UV exposure to orchestrate light-avoidance behaviour.

neuroscience↗

bioRxiv2023

Large-scale deorphanization of Nematostella vectensis neuropeptide GPCRs supports the independent expansion of bilaterian and cnidarian peptidergic systems

Neuropeptides are ancient signaling molecules in animals but only few peptide receptors are known outside bilaterians. Cnidarians possess a large number of G protein-coupled receptors (GPCRs) - the most common receptors of bilaterian neuropeptides - but most of these remain orphan with no known ligands. We searched for neuropeptides in the sea anemone Nematostella vectensis and created a library of 64 peptides derived from 33 precursors. In a large-scale pharmacological screen with these peptides and 161 N. vectensis GPCRs, we identified 31 receptors specifically activated by one of 14 peptides. Mapping GPCR and neuropeptide expression to single-cell sequencing data revealed how cnidarian tissues are extensively connected by multilayer peptidergic networks. Phylogenetic analysis identified no direct orthology to bilaterian peptidergic systems and supports the independent expansion of neuropeptide signaling in cnidarians from a few ancestral peptide-receptor pairs.

neuroscience↗

bioRxiv2023

A ciliary photoreceptor-cell circuit mediates pressure response in marine zooplankton

Hydrostatic pressure is a dominant environmental cue for vertically migrating marine organisms but the physiological mechanisms of responding to pressure changes remain unclear. Here we uncovered the cellular and circuit bases of a barokinetic response in the planktonic larva of the marine annelid Platynereis dumerilii. Increased pressure induced a rapid, graded and adapting upward swimming response due to the faster beating of cilia in the head multiciliary band. By calcium imaging, we found that brain ciliary photoreceptors showed a graded response to pressure changes. The photoreceptors in animals mutant for ciliary opsin-1 had a smaller sensory compartment and mutant larvae showed diminished pressure responses. The ciliary photoreceptors synaptically connect to the head multiciliary band via serotonergic motoneurons. Genetic inhibition of the serotonergic cells blocked pressure-dependent increases in ciliary beating. We conclude that ciliary photoreceptors function as pressure sensors and activate ciliary beating through serotonergic signalling during barokinesis.

animal behavior and cognition↗

bioRxiv2023

Evolution of the ribbon-like organization of the Golgi apparatus in animal cells

The Golgi ribbon is a structural organization formed by linked Golgi stacks that is believed to be exclusive to vertebrate cells. Its functional contribution to cellular processes is unclear, yet its disruption is associated with several human pathologies. In this study we address the evolutionary origin of the Golgi ribbon, describe a potential molecular mechanism for its emergence and identify a cellular process in which it may be involved. We observed the ribbon-like architecture in the cells of several metazoan taxa, suggesting its early appearance during animal evolution before the emergence of vertebrates. Supported by AlphaFold2 modelling, we propose that the evolution of the complex between two Golgi resident proteins, Golgin-45 and GRASP, led to the tethering of Golgi stacks into the ribbon-like configuration. Finally, we find that the ribbon is assembled during the early embryogenesis of deuterostome animals, a strong indication of its role in development. Overall, our study indicates that the Golgi ribbon is functionally relevant beyond vertebrates and calls for further investigations to decipher its elusive functions. O_FIG O_LINKSMALLFIG WIDTH=89 HEIGHT=200 SRC="FIGDIR/small/528797v2_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@17a404forg.highwire.dtl.DTLVardef@11413b4org.highwire.dtl.DTLVardef@119c036org.highwire.dtl.DTLVardef@19a512f_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG

cell biology↗

bioRxiv2023

Single-cell atlases of two lophotrochozoan larvae highlight their complex evolutionary histories

Pelagic larval stages are widespread across animals, yet it is unclear if larvae were present in the last common ancestor of animals or whether they evolved multiple times due to common selective pressures. Many marine larvae are at least superficially similar, they are small, swim through beating of ciliated bands and sense the environment with an apical organ structure. To understand these similarities, we have generated single cell atlases for marine larvae from two animal phyla and have compared their cell types. We found clear similarities among ciliary band cells and neurons of the apical organ in the two larvae pointing to possible homology of these structures suggesting a single origin of larvae within the clade analysed here (Lophotrochozoa). We also find several clade specific innovations in each larva, including distinct myocytes and shell gland cells in the oyster larva. Oyster shell gland cells express many novel genes which have made previous gene age estimates for trochophore larvae too young.

evolutionary biology↗

bioRxiv2022

Ciliary propulsion and metachronal coordination in reef coral larvae

Larval dispersal is critical to the survival of coral reefs. As the only motile stage of the reproductive cycle, coral larvae choose a suitable location to settle and mature into adult corals. Here, we present the first detailed study of ciliary propulsion in the common stony reef coral Acropora millepora. Using high-speed, high-resolution imaging, particle image velocimetry, and electron microscopy, we reveal the arrangement of the densely packed cilia over the larval body surface, and their organisation into diaplectic (transversely propagating) metachronal waves. We resolve the individual-ciliums beat dynamics and compare the resultant flows with a computational model of a ciliary array, and show that this form of ciliary metachronism leads to near-maximal pumping efficiency.

biophysics↗

bioRxiv2021

Pre-metazoan origin of neuropeptide signalling

Neuropeptides are a diverse class of signalling molecules in metazoans. They occur in all animals with a nervous system and also in neuron-less placozoans. However, their origin has remained unclear because no neuropeptide shows deep homology across lineages and none have been found in sponges. Here, we identify two neuropeptide precursors, phoenixin and nesfatin, with broad evolutionary conservation. By database searches, sequence alignments and gene-structure comparisons we show that both precursors are present in bilaterians, cnidarians, ctenophores and sponges. We also found phoenixin and a secreted nesfatin precursor homolog in the choanoflagellate Salpingoeca rosetta. Phoenixin in particular, is highly conserved, including its cleavage sites, suggesting that prohormone processing occurs also in choanoflagellates. In addition, based on phyletic patterns and negative pharmacological assays we question the originally proposed GPR-173 (SREB3) as a phoenixin receptor. Our findings indicate that signalling by secreted neuropeptide homologs has pre-metazoan origins and thus evolved before neurons.

genomics↗

bioRxiv2021

Desmosomal connectomics of all somatic muscles in an annelid larva

Cells form networks in animal tissues through synaptic, chemical and adhesive links. Invertebrate muscle cells often connect to other cells through desmosomes, adhesive junctions anchored by intermediate filaments. To study desmosomal networks, we skeletonised 853 muscle cells and their desmosomal partners in volume electron microscopy data covering an entire larva of the annelid Platynereis. Muscle cells adhere to each other, to epithelial, glial, ciliated, and bristle-producing cells and to the basal lamina, forming a desmosomal connectome of over 2,000 cells. The aciculae - chitin rods that form an endoskeleton in the segmental appendages - are highly connected hubs in this network. This agrees with the many degrees of freedom of their movement, as revealed by video microscopy. Mapping motoneuron synapses to the desmosomal connectome allowed us to infer the extent of tissue influenced by motoneurons. Our work shows how cellular-level maps of synaptic and adherent force networks can elucidate body mechanics.

animal behavior and cognition↗

bioRxiv2021

Nemertean, brachiopod and phoronid neuropeptidomics reveals ancestral spiralian signalling systems

Neuropeptides are diverse signalling molecules in animals commonly acting through G-protein coupled receptors (GPCRs). Neuropeptides and their receptors underwent extensive diversification in bilaterians and the relationships of many peptide-receptor systems have been clarified. However, we lack a detailed picture of neuropeptide evolution in lophotrochozoans as in-depth studies only exist for molluscs and annelids. Here we analyse peptidergic systems in Nemertea, Brachiopoda and Phoronida. We screened transcriptomes from thirteen nemertean, six brachiopod and four phoronid species for proneuropeptides and neuropeptide GPCRs. With mass spectrometry from the nemertean Lineus longissimus, we validated several predicted peptides and identified novel ones. Molecular phylogeny combined with peptide-sequence and gene-structure comparisons allowed us to comprehensively map spiralian neuropeptide evolution. We found most mollusc and annelid peptidergic systems also in nemerteans, brachiopods and phoronids. We uncovered previously hidden relationships including the orthologies of spiralian CCWamides to arthropod agatoxin-like peptides and of mollusc APGWamides to RGWamides from annelids, with orthologues systems in nemerteans, brachiopods and phoronids. We found that pleurin neuropeptides previously only found in molluscs are also present in nemerteans and brachiopods. We also identified cases of gene family duplications and losses. These include a protostome-specific expansion of RFamide/Wamide signalling, a spiralian expansion of GnRH-related peptides, and duplications of vasopressin/oxytocin before the divergence of brachiopods, phoronids and nemerteans. This analysis expands our knowledge of peptidergic signalling in spiralians and protostomes. Our annotated dataset of nearly 1,300 proneuropeptide sequences and 600 GPCRs presents a useful resource for further studies of neuropeptide signalling in protostomes.

evolutionary biology↗