Biology subjects

Guse, A.

Publications and source records attributed to Guse, A..

13 recordsLinked to original sources

bioRxiv2026

Domain-Specific Agonist Binding Affinities Explain Structural and Functional Regulation of TRPM2

TRPM2 is a Ca{superscript 2}-permeable cation channel activated by ADP-ribose (ADPR) and oxidative stress, yet the relative contributions of its two nucleotide-binding domains, MHR1/2 and NUDT9H, remain incompletely understood. Here, we quantitatively determine the affinities of the isolated human TRPM2 MHR1/2 and NUDT9H domains for ADPR, 2-deoxy-dADPR (dADPR), and 8-Br-cADPR using biophysical approaches. The MHR1/2 domain binds ADPR with high affinity (Kd {approx} 0.5 {micro}M), whereas the NUDT9H domain displays substantially lower affinity (Kd {approx} 192 {micro}M), revealing a difference of nearly three orders of magnitude. Mutational analysis demonstrates that alterations in MHR1/2 strongly affect ligand binding and channel activation, while mutations within NUDT9H that markedly reduce ligand affinity exert only modest effects on gating. In parallel, we quantify intracellular ADPR concentrations in resting and hydrogen peroxide-stimulated cells and find that they remain well below the affinity required for substantial NUDT9H occupancy. Together, our findings indicate that high-affinity binding to the MHR1/2 domain is sufficient to drive TRPM2 activation under physiological conditions, whereas the NUDT9H domain likely contributes to maintaining the structural integrity of the channel rather than directly mediating ligand-dependent activation. These results provide a quantitative framework for understanding ligand-dependent TRPM2 regulation in cells.

biophysics↗

bioRxiv2025

JPT2/HN1L functions as an NAADP-binding protein in a cell type-specific manner

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a second messenger evoking Ca2+ release from intracellular Ca2+ stores by targeting several Ca2+ channels, including two-pore channels (TPC1/2), transient receptor potential mucolipin-1 (TRPML1), or ryanodine receptor type 1 (RYR1). For activation of Ca2+ channels, NAADP requires binding proteins, such as JPT2/HN1L and LSM12. So far, their function has been analyzed in several cell lines and only a very limited number of primary cells; however, their physiological relevance in cell types known to utilize NAADP signaling remains unclear. Here, we generated Jpt2/Hn1l-/- mice to evaluate the contribution of JPT2/HN1L proteins to platelet aggregation and Ca2+ signaling in cardiomyocytes, mast cells, and T cells. NAADP is known to contribute to collagen-related peptide (CRP-XL)- evoked platelet aggregation, but this was not altered by JPT2/HN1L deletion. Functional Ca2+ imaging revealed that JPT2/HN1L plays a strikingly cell-type specific role in NAADP-mediated Ca2+ release. In electrically paced ventricular cardiomyocytes, {beta}-adrenergic stimulation is known to evoke arrhythmogenic spontaneous diastolic Ca2+ transients, which were not altered in their frequency in Jpt2/Hn1l-/- myocytes. Further, antigen-evoked Ca2+ transients in peritoneal mast cells (PMCs) are not changed in Jpt2/Hn1l-/- PMCs. However, CD4+ T cells displayed a pronounced requirement for JPT2/HN1L. Following T cell receptor/CD3 stimulation, global Ca2+ elevations and early NAADP-driven Ca2+ microdomains, which occur within tens of milliseconds of TCR/CD3 engagement and serve as initiating signals for downstream immune activation, were significantly decreased in Jpt2/Hn1l-/- CD4+ cells. We conclude that JPT2/HN1L is indispensable for NAADP-mediated Ca2+ release in T cells, but dispensable in cardiomyocytes, platelets, and mast cells, at least for the agonists employed. Accordingly, LSM12 might compensate for the loss of JPT2/HN1L. Together, JPT2/HN1L is not universally required as an NAADP-binding protein but exhibits cell-type specificity, with an essential function in T cell Ca2+ signaling.

pharmacology and toxicology↗

bioRxiv2025

Cross-Species Biomechanical Determinants of Shape Diversity

How complex molecular mechanisms translate into diverse multicellular shapes remains unclear. By leveraging the bi-layered architecture of six cnidarian species that diverged 500 million years ago, we show that modularity in supracellular mechanics governs larval shape diversity. Using active surface theory, quantitative imaging, and an inducible genetic system, we identify species-specific variations in three biomechanical modules. Basally aligned stress fibers drive axial elongation, while oral geometry and aboral rigidity define shape polarity. Remarkably, manipulating these modules transforms one species shape into another, demonstrating the causal relationship between module variation and shape diversity. Our analysis also uncovers instances of mechanical redundancies, where distinct module combinations generate similar shapes. These findings provide a general framework for how molecular complexity funnels into mesoscale mechanical determinants shaping morphological diversity.

developmental biology↗

bioRxiv2025

Symbiont-specific uptake is mediated by integrins in cnidarian larvae

The symbiotic relationship between dinoflagellate algae and their cnidarian hosts is fundamental to the health of coral reefs. The selection of appropriate symbionts is paramount for the host to gain valuable nutrients and could be tailored to increase stress tolerance against anthropogenic induced changes in ocean environments, such as coral bleaching in response to ocean warming. Previous research suggests glycan-lectin interactions play a role in symbiont uptake; however, blockage of such interactions does not fully inhibit symbiosis establishment, suggesting other receptors are at play. Potential candidates include RGD peptide binding integrins, which are known to mediate phagocytosis of microbes in other systems. Here, we used a combination of cnidarian model systems and human cell lines to determine if integrins facilitate symbiont recognition and uptake. Integrins are highly expressed in the endodermal tissue of the host, where symbiosis takes place, and upon uptake into endodermal cells, symbionts altered the expression of integrins and downstream signaling molecules. Blockage of integrin binding sites with RGD competitor peptides reduced symbiont uptake, but had no effect on the general uptake of non-symbiotic algae, or uptake in a non-symbiotic cnidarian. In addition, inert beads coated with integrin RGD peptide ligands were phagocytosed more readily than beads coated with scrambled peptide. Finally, overexpression of RGD-binding integrins in human cells increased symbiont uptake and mutation of the active binding site abolished uptake. Our findings reveal RGD-binding integrins as key players in symbiosis establishment and shed light on the evolutionary functions of integrins as phagocytic receptors. Significance statementCorals engage in a symbiotic partnership with photosynthetic algae to survive in challenging environments. To date it is largely unclear how the two partners recognize each other. Using a comparative model systems approach, we have identified evolutionary conserved integrins as molecular receptors for specifically engulfing symbionts, but not other algae. This suggests that integrins allow the host to distinguish between symbiotic and non-symbiotic algae and preferentially take up symbionts. Our findings establish a new paradigm for symbiosis establishment in corals and shed light on the ancient function of integrins as environmental sensors.

cell biology↗

bioRxiv2023

A predatory gastrula leads to symbiosis-independent settlement in Aiptasia

The planulae larvae of cnidarians (jellyfish, hydras, anemones, corals) have attracted interest since Haeckels 150-year-old postulation of the gastrula developmental stage of sponges and corals as the terminal lifeform of primitive multicellular metazoans. Widely viewed as primarily particle feeders, the planulae larvae of the anemone Exaiptasia pallida (commonly Aiptasia) have not been reported to undergo settlement and metamorphosis to adult morphology, and the lack of a closed lifecycle has been a major obstacle in this increasingly popular model system for coral-dinoflagellate endosymbiosis. Here we studied Aiptasia larvae feeding behavior and show its indispensability to trigger the first reports of settlement and metamorphosis in the system, finally closing the Aiptasia lifecycle. Surprisingly, the young gastrula-like planulae at just two days post fertilization actively feed on living crustacean nauplii, preferentially to heat-killed ones. Predation is dependent on functional stinging cells (nematocytes), indicative of complex neuronal control. Larvae fed daily dramatically increase in size and at 14 days post fertilization begin to morphologically change prior to settlement at high efficiency. Strikingly, dinoflagellate endosymbionts are neither required for larval growth nor measurably affect settlement dynamics, but are essential for spawning of the mature adult polyps. Our data show for the first time that gastrula-like planulae were capable of prey capture, suggesting carnivory in addition to filter feeding as a common strategy of this terminal life form. These data are discussed in the context of recent revelations on the evolution of basal metazoans.

zoology↗

bioRxiv2023

The cellular basis of feeding-dependent body size plasticity in sea anemones

Animals with indeterminate growth can adapt their growth rate and body size to changing food availability throughout their lifetime. As the cellular basis underlying food-dependent growth plasticity is poorly understood, we quantified how the sea anemones Nematostella vectensis and Exaiptasia diaphana (Aiptasia) respond to feeding and starvation on organismal and cellular levels. Using mathematical modelling to analyse growth phases, we found that growth and shrinkage rates in Nematostella are exponential, stereotypic and accompanied by high levels of cell gain or loss, respectively. During starvation and re-feeding, a considerable proportion of juvenile polyp cells (>7%) reversibly shift between S/G2/M and G1/G0 cell cycle phases, suggesting a tight nutritional control of quiescence and cell cycle re-entry. In the facultative symbiotic sea anemone Aiptasia, we found that growth and cell proliferation rates are dependent on the symbiotic state and, in comparison to Nematostella, respond less strongly to changes in food supply. Altogether, we provide a benchmark and resource to study the nutritional regulation of body plasticity on molecular, cellular and genomic levels using the rich functional toolkit available for Nematostella. Summary statementFeeding and starvation in sea anemones induce growth and shrinkage, cell size changes and dynamic cell proliferation changes that support a nutritional control of quiescence and cell cycle re-entry.

developmental biology↗

bioRxiv2020

Photoreceptor complexity accompanies adaptation to challenging marine environments in Anthozoa

Light represents a key environmental factor, which shapes the physiology and evolution of most organisms. Notable illustrations of this are reef-building corals (Anthozoa), which adapted to shallow, oligotrophic, tropical oceans by exploiting light from the sun and the moon to regulate various aspects of physiology including sexual reproduction, phototaxis and photosymbiosis. Together with the Medusozoa, (including jellyfish), the Anthozoa constitute the ancestral metazoan phylum cnidaria. While light perception in Medusozoa has received attention, the mechanisms of light sensing in Anthozoa remain largely unknown. Cnidaria express two principle groups of light-sensing proteins: opsins and photolyases/cryptochromes. By inspecting the genomic loci encoding these photoreceptors in over 35 cnidarian species, we reveal that Anthozoa have substantially expanded and diversified their photoreceptor repertoire. We confirm that, in contrast to Medusozoa, which retained one opsin class, anthozoans possess all three urmetazoan opsin classes. We show that anthozoans also evolved an extra sub-group (actinarian ASO-IIs). Strikingly, we reveal that cryptochromes including CRY-IIs are absent in Medusozoa, while the Anthozoa retained these and evolved an additional, novel cryptochrome class (AnthoCRYs), which contain unique tandem duplications of up to 6 copies of the PHR region. We explored the functionality of these photoreceptor groups by structure-function and gene expression analysis in the anthozoan model species Exaiptasia pallida (Aiptasia), which recapitulates key photo-behaviors of corals. We identified an array of features that we speculate reflect adaptations to shallow aquatic environments, moonlight-induced spawning synchronization and photosymbiosis. We further propose that photoreceptor complexity and diversity in Anthozoa reflects adaptation to challenging habitats.

evolutionary biology↗

bioRxiv2020

High temperature inhibits cnidarian-dinoflagellate symbiosis establishment through nitric oxide signaling

Disclaimer StatementThe authors have withdrawn their manuscript after further experiments based on reviewer comments did not support the conclusions of the paper. Therefore, the authors do not wish this work to be cited as reference for the project. The authors thank the anonymous reviewer for a critical assessment. If you have any questions, please contact the corresponding authors.

microbiology↗

bioRxiv2020

Controlling minimal and maximal hook-length of the bacterial flagellum

Hook-length control is a central checkpoint during assembly of the bacterial flagellum. During hook growth, a 405 amino acids (aa) protein, FliK, is intermittently secreted and thought to function as a molecular measuring tape that, in Salmonella, controls hook-length to 55 nm {+/-} 6 nm. The underlying mechanism involves interactions of both the -helical, N-terminal domain of FliK (FliKN) with the hook and hook cap, and of its C-terminal domain with a component of the export apparatus. However, various deletion mutants of FliKN display uncontrolled hook-length, which is not consistent with a ruler mechanism. Here, we carried out an extensive deletion analysis of FliKN to investigate its contribution in the hook-length control mechanism. We identified FliKN mutants deleted for up to 80 aa that retained wildtype motility. However, the short FliK variants did not produce shorter hook-lengths as expected from a physical ruler. Rather, the minimal length of the hook depends on the level of hook protein production and secretion. Our results thus support a model in which FliK functions as a hook growth terminator protein that limits the maximal length of the hook, and not as a molecular ruler that physically measures hook-length.

microbiology↗

bioRxiv2019

Dinoflagellate symbionts escape vomocytosis by host cell immune suppression

Emergence of the symbiotic lifestyle fostered the immense diversity of all ecosystems on Earth, but symbiosis plays a particularly remarkable role in marine ecosystems. Photosynthetic dinoflagellate endosymbionts power reef ecosystems by transferring vital nutrients to their coral hosts. The mechanisms driving this symbiosis, specifically those which allow hosts to discriminate between beneficial symbionts and pathogens, are not well understood. Here, we uncover that host immune suppression is key for dinoflagellate endosymbionts to avoid elimination by the host using a comparative, model systems approach. Unexpectedly, we find that the clearance of non-symbiotic microalgae occurs by non-lytic expulsion (vomocytosis) and not intracellular digestion, the canonical mechanism used by professional immune cells to destroy foreign invaders. We provide evidence that suppression of TLR signalling by targeting the conserved MyD88 adapter protein has been co-opted for this endosymbiotic lifestyle, suggesting that this is an evolutionarily ancient mechanism exploited to facilitate symbiotic associations ranging from coral endosymbiosis to the microbiome of vertebrate guts.

microbiology↗

bioRxiv2019

Nutrient-dependent mTORC1 signaling in coral-algal symbiosis

To coordinate development and growth with nutrient availability, animals must sense nutrients and acquire food from the environment once energy is depleted. A notable exception are reef-building corals that form a stable symbiosis with intracellular photosynthetic dinoflagellates (family Symbiodiniaceae (LaJeunesse et al., 2018)). Symbionts reside in symbiosomes and transfer key nutrients to support nutrition and growth of their coral host in nutrient-poor environments (Muscatine, 1990; Yellowlees et al., 2008). To date, it is unclear how symbiont-provided nutrients are sensed to adapt host physiology to this endosymbiotic life-style. Here we use the symbiosis model Exaiptasia pallida (hereafter Aiptasia) to address this. Aiptasia larvae, similar to their coral relatives, are naturally non-symbiotic and phagocytose symbionts anew each generation into their endodermal cells (Bucher et al., 2016; Grawunder et al., 2015; Hambleton et al., 2014). Using cell-specific transcriptomics, we find that symbiosis establishment results in downregulation of various catabolic pathways, including autophagy in host cells. This metabolic switch is likely triggered by the highly-conserved mTORC1 (mechanistic target of rapamycin complex 1) signaling cascade, shown to integrate lysosomal nutrient abundance with animal development (Perera and Zoncu, 2016). Specifically, symbiosomes are LAMP1-positive and recruit mTORC1 kinase. In symbiotic anemones, mTORC1 signaling is elevated when compared to non-symbiotic animals, resembling a feeding response. Moreover, symbiosis establishment enhances lipid content and cell proliferation in Aiptasia larvae. Challenging the prevailing belief that symbiosomes are early arrested phagosomes (Mohamed et al., 2016), we propose a model in which symbiosomes functionally resemble lysosomes as core nutrient sensing and signaling hubs that have co-opted the evolutionary ancient mTORC1 pathway to promote growth in endosymbiotic cnidarians.

cell biology↗

bioRxiv2018

Enhanced Stability of Non-Canonical NPC2 in the symbiosome supports coral-algal symbiosis

Cnidarians such as reef-building corals depend upon nutrient transfer from intracellular symbionts, but the mechanisms and evolution of this process remain unknown. Homologues of the conserved cholesterol binder Niemann-Pick Type C2 (NPC2) in cnidarians are implicated in the transfer of sterol from symbionts. Here, we show that symbionts transfer bulk sterols to the host, host sterol utilization is plastic, and pharmacological inhibition of sterol trafficking disrupts symbiosis. Having undergone an anthozoan-specific expansion, \"non-canonical\" NPC2s respond to symbiosis and accumulate over time at the lysosomal-like organelle in which the symbiont resides (\"symbiosome\"). We demonstrate that both a non- and canonical Aiptasia NPC2 bind symbiont-produced sterols, yet only the non-canonical homologue exhibits increased stability at low pH. We propose that symbiotic cnidarians adapted pre-existing cholesterol-trafficking machinery to function in the highly acidic symbiosome environment, allowing corals to dominate nutrient-poor shallow tropical seas worldwide.

cell biology↗

bioRxiv2017

Microinjection to deliver protein and mRNA into zygotes of the cnidarian endosymbiosis model Aiptasia sp.

Reef-building corals depend on an intracellular symbiosis with photosynthetic dinoflagellates for their survival in nutrient-poor oceans. Symbionts are phagocytosed by coral larvae from the environment and transfer essential nutrients to their hosts. Aiptasia, a small tropical marine sea anemone, is emerging as a tractable model system for coral symbiosis; however, to date functional tools and genetic transformation are lacking. Here we have established an efficient workflow to collect Aiptasia eggs for in vitro fertilization and microinjection as the basis for experimental manipulations in the developing embryo and larvae. We demonstrate that protein, mRNA, and DNA can successfully be injected into live Aiptasia zygotes to label actin with recombinant Lifeact-eGFP protein; to label nuclei and cell membranes with NLS-eGFP and farnesylated mCherry translated from injected mRNA; and to transiently drive transgene expression from an Aiptasia-specific promoter, respectively, in embryos and larvae. These proof-of-concept approaches pave the way for future functional studies of development and symbiosis establishment in Aiptasia, a powerful model to unravel the molecular mechanisms underlying intracellular coral-algal symbiosis.\n\nSummary StatementToolkit extension: development of microinjection for cellular labelling, expression of exogenous genes and live imaging in Aiptasia, an emerging model for intracellular coral-algal symbiosis.

developmental biology↗