Biology subjects

Ewer, J.

Publications and source records attributed to Ewer, J..

5 recordsLinked to original sources

bioRxiv2025

The olfactory organ is a site for neuroendocrine modulation of reproduction in zebrafish

Gonadotropin-releasing hormone (GnRH) is one of the most fascinating neuroendocrine peptides: It is essential for maintaining the reproductive state of vertebrates and also displays high sequence homology to the tridecapeptide mating pheromone of the yeast, S. cerevisiae. In spite of its highly conserved role in vertebrate reproduction, recent studies in zebrafish show that the loss of function of genes encoding Gnrh isoforms does not cause infertility. Here we first investigated whether Phoenixin, a novel peptide acting in the reproductive pathway of vertebrates, is the hormone that has replaced Gnrh in zebrafish. While loss of function of the phoenixin gene affected female differentiation, we observed no defects in fertility. We next reconsidered the GnRH pathway and turned to the natural world, where fishes use waterborne hormones to control reproduction. Thus, we investigated whether exogenous Gnrh affects the hypothalamic-pituitary axis. Here we show that fish isolated from their conspecifics and kept in artificial water devoid of fish odors, mounted sex-appropriate pituitary responses when Gnrh was added to the water. Furthermore, blocking the access of water to the olfactory organs eliminated these responses. We then analyzed Gnrh signaling by knocking out the gene encoding gnrh-receptor3 (gnrh-r3) and, surprisingly, found that fish homozygous for a gnrh-r3 null mutation were almost completely infertile: males did not produce sperm and females produced but a few mature oocytes. Finally, we found that Gnrh was present in nanomolar concentrations in the water that houses the fish, thus supporting the hypothesis that waterborne Gnrh from conspecifics plays a key role in regulating zebrafish reproduction in the absence of the endogenous ligand.

neuroscience↗

bioRxiv2025

Characterization Eclosion Hormone Receptor function reveals differential hormonal control of ecdysis during Drosophila development.

Neuromodulators and peptide hormones play important roles in regulating animal behavior. A well-studied example is ecdysis, which is used by insects to shed their exoskeleton at the end of each molt. Ecdysis is initiated by Ecdysis Triggering Hormone (ETH) and Eclosion Hormone (EH), which interact via positive feedback to coordinate the sequence of behavioral and physiological changes that cause exoskeleton shedding. Whereas the cell types targeted by ETH are well characterized, those targeted by EH have remained largely unknown due to limited characterization of the EH receptor (EHR). A gene encoding an EHR has been described in the oriental fruit fly, B. dorsalis, and in the desert locust, Schistocerca gregaria. However, little is known in these species about its expression pattern and its precise role at ecdysis, and no other insect EHRs are known. Here we analyze CG10738, the Drosophila ortholog of the B. dorsalis gene encoding EHR, and show that expressing it in cells confers sensitivity to EH. In addition, mutations of CG10738 specifically disrupt ecdysis, phenocopying the knockout of the EH gene. Together, these results indicate that CG10738 encodes the Drosophila EHR. As in B. dorsalis, EHR is expressed in the ETH-producing Inka cells; in addition, it is expressed in many known targets of ETH, including the neurons responsible for the secretion of other ecdysis-related peptides, such as CCAP and EH itself. Our results from targeted knockdown and rescue experiments reveal that EHR is required for ecdysis in diverse cell types and that the role of EHR in different targets differs with developmental stage. Our findings indicate extensive convergence of EH and ETH signaling and provide an exemplar of the complex mechanisms by which hormones control animal behavior. AUTHOR SUMMARYHormones and neuromodulators are important regulators of animal behavior. In insects, one of the best studied behaviors influenced by hormones is ecdysis, which allows the animal to shed the remains of its exoskeleton at the end of each molt. Ecdysis is controlled by two key hormones: Ecdysis Triggering Hormone (ETH) and Eclosion Hormone (EH). Whereas most targets of ETH have been identified, those of EH have remained largely unknown due to the limited characterization of its receptor, EHR. Previous studies identified a gene encoding EHR in the oriental fruit fly, Bactrocera dorsalis, and in the desert locust, Schistocerca gregaria, but little is known about its expression pattern or its precise role. Here, we show that CG10738 encodes the Drosophila EHR. We found that EHR is expressed in ETH-producing Inka cells, in neurons that secrete other ecdysis-related peptides, in addition to other neuronal classes and non-neuronal cells. Targeted knockdown and rescue experiments revealed that EHR is essential for ecdysis in various cell types, and that its role can vary depending on the developmental stage. Our findings reveal that the role of EH at ecdysis is complex and provides insights into how hormones and neuromodulators regulate animal behavior.

neuroscience↗

bioRxiv2025

Synaptic Targets of Circadian Clock Neurons Influence Core Clock Parameters

Neuronal connectivity in the circadian clock network is essential for robust endogenous timekeeping. In the Drosophila circadian clock network, four pairs of small ventral lateral neurons (sLNvs) serve as critical pacemakers. Peptidergic communication via sLNv release of the key output neuropeptide Pigment Dispersing Factor (PDF) has been well characterized. In contrast, little is known about the role of the synaptic connections that sLNvs form with downstream neurons. Connectomic analyses revealed that the sLNvs form strong synaptic connections with a group of previously uncharacterized neurons, SLP316. Here, we show that silencing synaptic output in the SLP316 neurons via tetanus toxin (TNT) expression shortens the free-running period, whereas hyper-exciting them by expressing the Na[+] channel NaChBac results in period lengthening. Under light-dark cycles, silencing SLP316 neurons also causes lower daytime activity and higher daytime sleep. Our results revealed that the main postsynaptic partners of the Drosophila pacemaker neurons are a non-clock neuronal cell type that regulates the timing of sleep and activity.

neuroscience↗

bioRxiv2023

Timed receptor tyrosine kinase signaling couples the central and a peripheral circadian clock in Drosophila

Circadian clocks impose daily periodicities to behavior, physiology, and metabolism. This control is mediated by a central clock and by peripheral clocks, which are synchronized to provide the organism with a unified time through mechanisms that are not fully understood. Here, we characterized in Drosophila the cellular and molecular mechanisms involved in coupling the central clock and the peripheral clock located in the prothoracic gland (PG), which together control the circadian rhythm of emergence of adult flies. The time signal from central clock neurons is transmitted via small neuropeptide F (sNPF) to neurons that produce the neuropeptide Prothoracicotropic Hormone (PTTH), which is then translated into circadian oscillations of Ca2+ concentration and daily changes in PTTH levels. Rhythmic PTTH signaling is required at the end of metamorphosis, and transmits time information to the PG by imposing a daily rhythm to the expression of the PTTH receptor tyrosine kinase (RTK), TORSO, and of ERK phosphorylation, a key component of PTTH transduction. In addition to PTTH, we demonstrate that signaling mediated by other RTKs contribute to the rhythmicity of emergence. Interestingly, the ligand to one of these receptors (Pvf2), plays an autocrine role in the PG, which may explain why both central brain and PG clocks are required for the circadian gating of emergence. Our findings show that the coupling between the central and the PG clock is unexpectedly complex and involves several RTKs that act in concert, and could serve as a paradigm to understand how circadian clocks are coordinated. Significance statementCircadian clocks impose daily periodicities to behavior, physiology, and metabolism, and are synchronized to provide the organism with a unified time through mechanisms that are poorly understood. In holometabolous insects, the circadian control of adult emergence depends on the coupling between the central clock and a peripheral clock located in the prothoracic gland (PG). Here we identify the cellular and molecular mechanism that transmits time information from the central clock to the PG clock. This process is unexpectedly complex and involves a number of receptor tyrosine kinases (RTKs). Such a mechanism may add robustness to the coupling between the 2 clocks and serve as a paradigm for understanding how circadian clocks are coordinated.

neuroscience↗

bioRxiv2021

Extracting temporal relationships between weakly coupled peptidergic and motoneuronal signaling: application to Drosophila ecdysis behavior

Neuromodulators, such as neuropeptides, can regulate and reconfigure neural circuits to alter their output, affecting in this way animal physiology and behavior. The interplay between the activity of neuronal circuits, their modulation by neuropeptides, and the resulting behavior, is still poorly understood. Here, we present a quantitative framework to study the relationships between the temporal pattern of activity of peptidergic neurons and of motoneurons during Drosophila ecdysis behavior, a highly stereotyped motor sequence that is critical for insect growth. We analyzed, in the time and frequency domains, simultaneous intracellular calcium recordings of peptidergic CCAP (crustacean cardioactive peptide) neurons and motoneurons obtained from isolated central nervous systems throughout fictive ecdysis behavior induced ex vivo by Ecdysis triggering hormone. We found that the activity of both neuronal populations is tightly coupled in a cross-frequency manner, suggesting that CCAP neurons modulate the faster oscillation of motoneurons. To explore this idea further, we used a probabilistic logistic model to show that calcium dynamics in CCAP neurons can predict the oscillation of motoneurons, both in a simple model and in a conductance-base model capable of simulating many of the observed neural dynamics features. Finally, we developed an algorithm to quantify the motor behavior observed in videos of pupal ecdysis, and compared their features to the patterns of neuronal calcium activity recorded ex vivo. We found that the motor activity of the intact animal is more regular than the motoneuronal activity recorded from the ex vivo preparations during fictive ecdysis behavior; the analysis of movement patterns also allowed us to identify a new post-ecdysis phase. Author SummaryRepetitive movements such as walking, swimming, and flying are controlled by networks of neurons known as central patter generators. In many cases, the exact pattern of activity is modulated by neuropeptides, which are small signaling molecules that, unlike neurotransmitters, are broadly released within regions of the nervous system. Because of this mode of action, it can be difficult to discern the relationship between the temporal pattern of firing of peptidergic neurons and the timing of the resulting motor behavior. Here, we developed methods to analyze the patterns of activity of such weakly coupled systems as applied to ecdysis, the stereotyped sequence of behaviors used by insects to shed the remains of their old exoskeleton at the end of every molt. Key actors in this process are motoneurons (MN) and a set of neurons expressing the neuropeptide, Crustacean Cardioactive Peptide (CCAP). Combining real-time calcium imaging, frequency analysis, computational simulations, and image processing, we determined the relationships between the activity of CCAP neurons and the resulting motor output during pupal ecdysis in the fruit fly, Drosophila melanogaster. We found that several temporal features of the activity of CCAP neurons are highly coupled to the patter of activity motoneuronal pattern, suggesting an active role of CCAP neurons during ecdysis. We also developed quantitative approaches that allowed us to identify a new ecdysis sub-phase.

neuroscience↗