Biology subjects

Chatzigeorgiou, M.

Publications and source records attributed to Chatzigeorgiou, M..

15 recordsLinked to original sources

bioRxiv2026

Developmental genetic response of the zooplanktonic tunicate Oikopleura dioica to marine noise pollution.

BackgroundAnthropogenic noise is an emerging threat to marine ecosystems, yet its effects on marine invertebrates, particularly zooplanktonic species, remain poorly understood. Despite increasing evidence of behavioral and physiological impacts in invertebrates, the effects of noise on embryonic development and the molecular mechanisms underlying acoustic responses remain largely unexplored. Here, to address this gap, we investigated the impact of high-intensity underwater noise exposure on embryogenesis of the appendicularian tunicate Oikopleura dioica, a cosmopolitan zooplanktonic tunicate that plays important ecological roles in marine trophic webs and carbon cycling. Under lab-controlled conditions, we examined the effects of experimental noise exposure on early embryogenesis at both morphological and transcriptomic levels using RNA-seq in 8-cell (8c) and early tailbud (ETB) stages. ResultsNoise exposure produced no significant increase in embryo malformations compared to non-exposed controls, indicating substantial phenotypic resilience under laboratory conditions. Interestingly, transcriptomic analyses revealed a rapid molecular response of 70 differentially expressed genes (DEG) already detectable after only 30 minutes of exposure at the 8-cell stage, which became markedly amplified with 700 DEGs by the ETB stage. Together, differential expression, GO enrichment, and co-expression network analyses identified coordinated regulation of processes associated with membrane homeostasis, pyrimidine/CTP metabolism, extracellular matrix organization, cytoskeletal architecture, RNA regulation, translational control, proteostasis, mitochondrial metabolism, and developmental pathways. Importantly, both developmental stages precede the formation of differentiated mechanosensory structures, suggesting that the observed responses are unlikely to reflect conventional sound perception. ConclusionsThese findings provide the first molecular characterization of noise effects during O. dioica embryogenesis and reveal an unexpected molecular sensitivity of O. dioica embryos to underwater noise despite preserved morphological development. The transcriptional signatures support a mechanobiological framework in which acoustic exposure may directly perturb cellular mechanical homeostasis through membrane-and cytoskeleton-associated processes, triggering compensatory stress-adaptation responses involving proteostasis, RNA regulation, and metabolic reprogramming. Together, these findings establish O. dioica as a valuable emerging model for investigating the developmental and evolutionary consequences of acoustic pollution in marine ecosystems.

developmental biology↗

bioRxiv2025

Behavioral ontogeny in a pelagic tunicate reveals the deep origins of chordate behavioral developmental plasticity.

Behavioral developmental plasticity refers to the lasting changes in an organisms behavior that occur during development in response to external and internal cues, enhancing survival and reproduction. While well studied in vertebrates, its occurrence in other chordates, including tunicates, the closest relatives of vertebrates, remains unclear. We built a behavioral atlas of the planktonic tunicate Oikopleura dioica across its life cyclefrom larval to adult stages using high-throughput tracking and unsupervised analysis. Swimming kinematics, exploration, and thigmotaxis increased with development. Adults exhibit a unique innovation, known as the house, a complex extracellular filtration structure encasing the animal trunk, which drastically alters locomotion and exploration compared to free-swimming individuals. Postural variation during ontogeny is captured by seven basic shapes ("eigenoikopleuras"), with complex shapes becoming more frequent over time. Spatiotemporal embedding and Hidden Markov modeling revealed that behavioral refinement arises from changes in motor modules and their transitions. House occupancy similarly shifts these modules, indicating context-specific specialization. This continuous behavioral maturation parallels Oikopleuras neotenic morphology, retaining a larval body plan unlike other tunicates. Our atlas provides a quantitative framework for exploring the evolution of behavioral developmental plasticity in chordates.

animal behavior and cognition↗

bioRxiv2025

The evolution of embodied postural dynamics underlies behavioral diversity in benthic sessile chordate

Benthic animals live on or in the seafloor, a habitat known as the benthic zone. These bottom-dwelling organisms account for the largest fraction of animal diversity in our seas, playing vital roles in nutrient cycling, sediment stabilization and the broader food webs. Historically, the behavioral repertoire of benthic animals attached permanently to the sea floor has been considered as extremely limited (if at all present), reflecting an evolutionary adaptation to their sessile lifestyle and simplified nervous systems. Here, we overturn this view by studying the spontaneous and stimulus evoked behavioral repertoire of the basal chordate Ciona intestinalis which has a benthic sessile adult stage. We found that Ciona adults transition between three main postural engagement behavioral states. These are defined by different body part kinematics and postural dynamics characterised by changes in body shape configuration as opposed to locomotion. Transitions between states can occur probabilistically in spontaneously behaving animals suggesting that they can be internally generated by the simple brain of an adult Ciona. Importantly, using spatiotemporal embedding of postural features, we constructed a behavioral space for Ciona adults, which was divided into 18 stereotyped behavioral modes revealing the unappreciated richness of adult Ciona behaviors. Our analysis showed that Ciona adults can deploy in a selective manner these behavioral modules to elicit distinct responses to different mechanical stimuli, suggesting the presence of a sensory context dependent regulation of behavior in these benthic organisms. Our study raises the possibility that embodied postures is underlie the evolution of behavioral repertoires in sessile benthic animals.

animal behavior and cognition↗

bioRxiv2025

Mechanics regulate the postembryonic developmental maturation and function of sensory neurons in a pre-vertebrate chordate.

Physical forces are emerging as important contributors to a wide diversity of biological processes across multiple scales and contexts. The development of the nervous system is infuenced by mechanical forces exerted on neurons and glia by the surrounding environment. However, the extent to which tissue mechanics influence the function and morphology of the post-embryonic nervous system remains unclear. Here we leverage the post-embryonic larval period of the pre-vertebrate chordate Ciona intestinalis to study the dynamic interplay between nervous system mechanics, cellular and nuclear morphology and neuronal function. During this post-embryonic period the larval head undergoes substantial stretching along the anterior-posterior axis. We show that this macroscopic morphological change is associated with a significant change in cell and nuclear shape (stretching) of the polymodal sensory neurons located in the papillar organs. Using FRET based genetically encoded tension sensors we show that mechanical tension at the focal adhesions and the nuclear envelope of these papillar sensory neurons increases with time. At the functional level Ca2+ imaging experiments reveal that presentation and removal of a chemosensory stimulus that promotes settlement and metamorphosis elicits significantly stronger responses in late swimming larvae papillar neurons compared to those newly hatched ones. Finally, by combining optoGEF-RhoA dependent control of cellular forces and Ca2+ imaging we demonstrate that the strength of chemosensory responses and settlement behavior can be modulated by mechanical forces.

developmental biology↗

bioRxiv2025

The cellular and behavioral blueprints of chordate rheotaxis.

The oceans are filled with life-forms exhibiting complex adaptations to help navigate fluid environments and take advantage of fluid motion to locomote and disperse. However, the neuronal and behavioral underpinnings of navigating in fluid environments outside vertebrates are poorly understood. We present behavioral and computational modelling-based evidence that the pre-vertebrate chordate Ciona intestinalis actively modulates its heading and angular velocities to counter oncoming flows and perform positive rheotaxis. We demonstrate that a distributed network of ciliated peripheral sensory neurons is responsible for sensing hydrodynamic information such as flow velocity and direction. Pharmacological removal of sensory cilia impedes rheotactic behavior and reduces stimulus evoked neuronal activity. Whole-brain calcium imaging experiments reveal that the central nervous system of Ciona can encode the onset and offset of flow, flow direction, and flow velocity, suggesting that miniature chordate brain is capable of surprisingly sophisticated computations.

neuroscience↗

bioRxiv2024

Anoctamins mediate polymodal sensory perception and larval metamorphosis in a non-vertebrate chordate.

An exceptional feature of most animals is their ability to perceive diverse sensory cues from the environment and integrate this information in their brain to yield ethologically relevant behavioral output. For the myriad of marine species, the ocean represents a complex sensory environment, which acts as a crucible of evolution for polymodal sensory perception. The cellular and molecular bases of polymodal sensory perception in a marine environment remain enigmatic. Here we use Ca2+ imaging and quantitative behavioral analysis to show that in the tunicate Ciona intestinalis two members of the evolutionarily conserved Anoctamin family1-4 (Tmem16E/Ano5 and Tmem16F/Ano6), are required for sensing chemosensory and mechanosensory metamorphic cues. We find that they act by modulating neuronal excitability and Ca2+ response kinetics in the primary sensory neurons and axial columnar cells of the papillae, a widely conserved sensory-adhesive organ across ascidians5-9. Finally, we use electrophysiological recordings and a scramblase assay in tissue culture to demonstrate that Tmem16E/Ano5 acts as a channel, while Tmem16F/Ano6 is a bifunctional ion channel and phospholipid scramblase. Our results establish Ano5 and Ano6 as novel players in the zooplanktonic, pre-vertebrate molecular toolkit that controls polymodal sensory perception in aquatic environments.

neuroscience↗

bioRxiv2023

Pax37 gene function in Oikopleura dioica supports a neuroepithelial-like origin for its house-making Fol territory

Larvacean tunicates feature a spectacular innovation not seen in other animals - the trunk oikoplastic epithelium (OE). This epithelium produces a house, a large and complex extracellular structure used for filtering and concentrating food particles. Previously we have shown that several homeobox transcription factors may play a role in patterning the OE. Among these are two Pax3/7 duplicates that we named Pax37A and Pax37B. The vertebrate homologs, PAX3 and PAX7, are involved in developmental processes related to neural crest and muscles. In the ascidian tunicate Ciona robusta, Pax3/7 has been given a role in development of cells deriving from the neural plate border including trunk epidermal sensory neurons and tail nerve cord neurons as well as in neural tube closure. Here we have investigated the roles of Pax37A and Pax37B in the development of the OE using CRISPR-Cas9, analyzing scRNA-seq data from wild-type animals that were compared with scRNA-seq data from C. robusta. We revealed that Pax37B but not Pax37A is essential for the differentiation of cell fields that produce the food concentrating filter of the house: the anterior Fol, giant Fol and Nasse cells. Lineage analysis supports that expression of Pax37 is under influence of Wnt signaling and that Fol cells have a neuroepithelial-like transcriptional signature. We propose that the highly specialized secretory epithelial cells of the Fol region either maintained or evolved neuroepithelial features as do "glue" secreting collocytes of ascidians. Their development seems to be controlled by a GRN that also operates in some ascidian neurons.

developmental biology↗

bioRxiv2023

Polymodal sensory perception of mechanical and chemical cues drives robust settlement and metamorphosis of a marine pre-vertebrate zooplanktonic larva.

The Earths oceans brim with an incredible diversity of microscopic planktonic animals, many of which correspond to the transient larval stage in the life cycles of benthic marine organisms. The mechanisms by which marine larvae use their nervous system to sense and process diverse environmental cues (physical and chemical) in the water column and the benthos to settle and metamorphose is a major problem across the fields of neuroscience, development, evolution and ecology, yet they remain largely unclear. Here, we employ Ca2+ imaging and behavioral assays using the larval form of the protochordate Ciona intestinalis to characterise the mechanical and chemical stimuli these larvae respond to during settlement and metamorphosis. We also identify the polymodal sensory cells that detect these stimuli. Whole brain Ca2+ imaging further revealed that the presentation or removal of ethological chemosensory stimuli engages the activities of different neuronal sub-populations resulting in brain state changes, which may underlie behavioral action selections and metamorphosis. Finally, chemogenetic interrogation coupled to behavioral analysis reveals that peptidergic sensory neurons including polymodal cells capable of chemotactile perception and chemosensory/neurosecretory cells of proto-placodal ectoderm origin play a pivotal role in regulating stimulus induced settlement and metamorphosis. This work suggests that marine zooplanktonic larvae utilise their streamlined nervous systems to perform multimodal integration of ethologically physical and chemical cues to explore the oceanic water column and benthos.

neuroscience↗

bioRxiv2023

When offspring outsmarting parents: Neuronal genes expression in two generations of marine parasitic worm

Trematodes, or flukes, cause disease in millions of people, impact animal health, and alter the functional organization of biological communities. During the transition from the intramolluscan redia to the free-living cercaria stage in a complex life cycle of trematodes, extensive anatomical and behavioral modifications occur, enabling the cercaria to locate and infect the next host in the complex water environment. However, the functional changes that occur in the nervous system during this shift are not well understood. We used a de novo transcriptome to characterize the molecular building blocks of the trematode nervous system and identify pathways that may underlie differences in nervous system function between the rediae and cercariae stages of the Cryptocotyle lingua, marine trematode species causing problems for fisheries. Our results confirmed the streamlined molecular toolkit of these parasitic trematodes, including the absence of certain key signaling pathways and ion channels. We documented the loss of nitric oxide synthase not only in C. lingua but also in the entire phylum Platyhelminthes. We identified several neuronal genes upregulated in dispersal larvae, including genes involved in synaptic vesicle trafficking, TRPA channels, G-protein coupled receptors, and surprisingly nitric oxide receptors soluble guanylate cyclase. Validation of these findings using neuronal markers and in situ hybridization allowed us to hypothesize the protein function in relation to the adaptations and host-finding strategy of the dispersal larva. Our results and established behavior quantification toolkit for cercaria motility provide a foundation for future research on the behavior and physiology of parasitic flatworms, with potential implications for developing antiparasitic measures. HighlightsO_LIWe utilized a behavior quantification toolkit and described essential neuronal genes in a handy model species, enabling the study of fluke neurobiology at the systems level. C_LIO_LIWe characterized and validated neuronal gene expression profiles in cercarial embryos within rediae and swimming host-searching cercariae. C_LIO_LIThe streamlined molecular toolkit of parasites reveals the absence of important signaling pathways and ion channels in their nervous system. C_LIO_LIWe documented loss of nitric oxide synthase in flatworms. C_LIO_LIThe expression pattern of nitric oxide receptors, soluble guanylate cyclases, upregulated in swimming larvae, emphasizes their crucial involvement in the dispersal process. C_LIO_LITwo upregulated TRPA channels in cercaria are primarily expressed in cilia and peripheral neurons, emphasizing their importance in host finding. C_LI

zoology↗

bioRxiv2023

Anoctamin 10/TMEM16K mediates convergent extension and tubulogenesis during notochord formation in the early chordate Ciona intestinalis.

During embryonic development, cells are organized into complex tissues and organs. A highly conserved organ shape across metazoans is the epithelial tube. Tube morphogenesis is a complex multistep process where the molecular mechanisms underlying the diversity of cell behaviors such as convergent extension, cell elongation, and lumen formation are still intensely studied. Here, using genome editing and quantitative imaging in the early chordate Ciona intestinalis we show that Ano10/Tmem16k, a member of the evolutionarily ancient family of transmembrane proteins called Anoctamin/TMEM16 is required for convergent extension, lumen expansion and connection during notochord morphogenesis. In addition, we find that loss of Cii.Ano10/Tmem16k hampers cell behavior and cytoskeletal organization during tubulogenesis. In vivo Ca2+ imaging revealed that genetic ablation of Cii.Ano10/Tmem16k hinders the ability of notochord cells to regulate bioelectrical signaling. Finally, we use electrophysiological recordings and a scramblase assay in tissue culture to demonstrate that Cii.Ano10/Tmem16k likely acts as an ion channel but not as a phospholipid scramblase. More generally, this work provides insights into the pre-vertebrate functions of Anoctamins and raises the possibility that Anoctamin/Tmem16 family members have an evolutionarily conserved role in tube morphogenesis.

developmental biology↗

bioRxiv2021

Comprehensive analysis of behavioral dynamics in the protochordate Ciona intestinalis

Vertebrate nervous systems can generate a remarkable diversity of behaviors. However, our understanding of how behaviors may have evolved in the chordate lineage is limited by the lack of neuroethological studies leveraging our closest invertebrate relatives. Here we combine high-throughput video acquisition with pharmacological perturbations of bioamine signaling to systematically reveal the global structure of the motor behavioral repertoire in the Ciona intestinalis larvae. Most of Cionas postural variance can be captured by six basic shapes, which we term "Eigencionas". Motif analysis of postural time series further demonstrated that bioamines influence numerous stereotyped behavioral maneuvers including "startle-like" and "beat-and-glide". Employing computational modeling of swimming dynamics and spatio-temporal embedding of postural features revealed that subtle behavioural differences are generated at the levels of motor modules and the transitions between, both modulated by bioamines. Finally, we show that flexible motor module usage gives rise to diverse behaviors in response to different light stimuli.

animal behavior and cognition↗

bioRxiv2021

The unique neuronal structure and neuropeptide repertoire in the ctenophore Mnemiopsis leidyi shed light on the evolution of animal nervous systems

The ctenophore nerve net represents one of the earliest evolved nervous system of animals. Due to the uncertainties of their phylogenetic placement of ctenophores and the absence of several key bilaterian neuronal genes, it has been hypothesized that their neurons have evolved independently. Whether this is indeed the case remains unclear, and thus the evolutionary history of neurons is still contentious. Here, we have characterized the neuropeptide repertoire of the ctenophore Mnemiopsis leidyi. Using the machine learning NeuroPID tool1 129 new putative neuropeptide precursors were predicted. Sixteen of them are detected in the subepithelial nerve net (SNN), aboral organ (AO) and epithelial sensory cells (ESC) of early cydippid-stage M. leidyi by in situ hybridization (ISH) and immunohistochemistry (IHC). Four of these neuropeptides increase the animals swimming velocity in a behavioral essay. The new neuropeptides were used as markers to identify neuronal cell types in single cell transcriptomic data2. To unravel the neuronal architecture, we 3D reconstructed the SNN underlying the comb plates using serial block-face scanning electron microscopy (SBF-SEM). For the first time, we confirm a more than 100 years old hypothesis about anastomoses between neurites of the same cell in ctenophores and reveal that they occur through a continuous membrane. Our findings reveal the unique neuronal structure and neuropeptide repertoire of ctenophores and are important for reconstructing the evolutionary origin of animal neurons and nervous systems.

evolutionary biology↗

bioRxiv2020

Mapping calcium dynamics in a developing tubular structure.

Calcium is a ubiquitous and versatile second messenger that plays a central role in the development and function of a wide range of cell types, tissues and organs. Despite significant recent progress in the understanding of calcium (Ca2+) signalling in organs such as the developing and adult brain, we have relatively little knowledge of the contribution of Ca2+ to the development of tubes, structures widely present in multicellular organisms. Here we image Ca2+ dynamics in the developing notochord of Ciona intestinalis. We show that notochord cells exhibit distinct Ca2+ dynamics during specific morphogenetic events such as cell intercalation, cell elongation and tubulogenesis. We used an optogenetically controlled Ca2+ actuator to show that sequestration of Ca2+ results in defective notochord cell intercalation, and pharmacological inhibition to reveal that stretch-activated ion channels (SACs), inositol triphosphate receptor (IP3R) signalling, Store Operated Calcium Entry (SOCE), Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) and gap junctions are required for regulating notochord Ca2+ activity during tubulogenesis. Cytoskeletal rearrangements drive the cell shape changes that accompany tubulogenesis. In line with this, we show that Ca2+ signalling modulates reorganization of the cytoskeletal network across the morphogenetic events leading up to and during tubulogenesis of the notochord. We additionally demonstrate that perturbation of the actin cytoskeleton drastically remodels Ca2+ dynamics, suggesting a feedback mechanism between actin dynamics and Ca2+ signalling during notochord development. This work provides a framework to quantitatively define how Ca2+ signalling regulates tubulogenesis using the notochord as model organ, a defining structure of all chordates.

developmental biology↗

bioRxiv2019

Mesmerize: A highly versatile platform for calcium imaging analysis and creation of self-contained FAIR datasets.

Calcium imaging is an increasingly valuable technique for understanding neural circuits, neuroethology, and cellular mechanisms. The analysis of calcium imaging data presents challenges in image processing, data organization, analysis, and accessibility. Tools have been created to address these problems independently, however a comprehensive user-friendly package does not exist. Here we present "Mesmerize", an efficient, expandable and user-friendly analysis platform, which uses a Findable, Accessible, Interoperable and Reproducible (FAIR) system to encapsulate the entire analysis process, from raw data to interactive visualizations for publication. Mesmerize provides a user-friendly graphical interface to state-of-the-art analysis methods for signal extraction & downstream analysis. We demonstrate the broad scientific scope of Mesmerizes applications by analyzing neuronal datasets from mouse and a volumetric zebrafish dataset. We also applied contemporary time-series analysis techniques to analyze a novel dataset comprising neuronal, epidermal, and migratory mesenchymal cells of the protochordate Ciona intestinalis.

neuroscience↗

bioRxiv2018

Quantitative analysis reveals the basic behavioural repertoire of the urochordate Ciona intestinalis.

Quantitative analysis of animal behaviour in model organisms is becoming an increasingly essential approach for tackling the great challenge of understanding how activity in the brain gives rise to behaviour. In addition, behavioural analysis can provide insight on the molecular basis of nervous system development and function as demonstrated by genetic screens focused on behavioural phenotyping in some genetically tractable model organisms. The progress in building low-cost automated tracking setups, together with advances in computer vision machine learning have expanded the repertoire of organisms which are amenable to quantitative behavioural analysis. Here we used automated image-based tracking to extract behavioural features from an organism of great importance in understanding the evolution of chordates, the free swimming larval form of the tunicate Ciona intestinalis which has a compact and fully mapped nervous system composed of only 231 neurons. We analysed hundreds of videos of larvae and we extracted basic geometric and physical descriptors of larval behaviour. Most importantly, we used machine learning methods to create an objective ontology of behaviours for C. intestinalis larvae. We identified eleven behavioural modes using agglomerative clustering. This approach enabled us to produce a quantitative description of the basic larval behavioural repertoire. Furthermore, we tested the robustness of this repertoire by comparing different rearing conditions and ages. Using our pipeline for quantitative behavioural analysis, we successfully reproduced the known photoresponsive behaviour and the first demonstration to our knowledge that C. intestinalis larvae exhibit sensory arousal and thigmotaxis, both of which can be modulated by the anxiotropic drug modafinil. Remarkably, by comparing the behaviour between animals assayed individually or in small groups, we found that crowd size influences larval behaviour. This study shows that C. intestinalis larval behaviour can be broken down to a set of stereotyped behaviours that are used to different extents in a context-dependent manner. Furthermore, it raises exciting possibilities such as mapping behaviour to specific neurons of this compact chordate nervous system and it paves the way for comparative quantitative behavioural studies as a means to reconstruct the evolution of behaviour, especially in the chordate lineage.

animal behavior and cognition↗