Biology subjects

Hobmayer, B.

Publications and source records attributed to Hobmayer, B..

7 recordsLinked to original sources

bioRxiv2026

Ultrastructure of stemness and differentiated state in Hydra epithelial cells

Epithelial cells in Hydra perform an unusual combination of functions: they divide continuously like adult stem cells while simultaneously executing the complex physiological tasks of differentiated epithelia. This challenges the traditional distinction between proliferative stem cells and terminally differentiated tissue, raising the question of how a single cell type integrates these opposing roles. Using electron microscopy, we examined morphological characteristics that define the stem-like and differentiated states of Hydras ectodermal and endodermal epithelial cells. Stemness is reflected by nuclear characteristics of active proliferation, including extensive euchromatin, large nucleoli, and the presence of nuage. However, differentiated epithelial cells exhibit strong apical-basal polarity, various endomembrane compartments for endocytosis and transport, specialized secretion mechanisms, and basal muscle processes with dense-core vesicles implicated in hormonal communication. Cryofixation improved ultrastructure preservation, elucidating the pleiomorphic configurations of complex intracellular channel systems traditionally presenting as singular vacuoles. This may shed new light on possible functions of this compartment. Taken together, Hydra epithelial cells combine ancient stem cell traits with highly specialized differentiated functions. This multifunctionality provides insight into the cellular organization of early-branching animals and suggests that multifunctional epithelia may represent an ancestral condition preceding the strict segregation of stem and differentiated cell lineages in bilaterians.

evolutionary biology↗

bioRxiv2026

Structural assembly of the glycan-rich, chitin-reinforced adhesive of Hydra is coordinated by a lectin-like protein, HvAb1

Aquatic animals deploy adhesives, in numerous essential functions, and reversibility is a key adaptation. The molecular mechanisms of reversible wet adhesion remain poorly understood. Using a model organism, the freshwater cnidarian Hydra vulgaris, we dissect the mechanism of molecular assembly in a secreted adhesive and uncover a glycan and protein-based architecture organized by a lectin-like protein, Hydra vulgaris adhesive protein 1 (HvAb1). We identify HvAb1 as a nonredundant organizer of the adhesive matrix, being basal-disc specific and secreted. Knockdown of HvAb1 severely impaired attachment and disrupted footprint architecture in a mosaic pattern, with only HvAb1-positive regions of the adhesive footprint retaining their normal structure. The adhesive is wheat germ agglutinin (WGA)-reactive and contains a fibrillar chitin-based sub-network, synthesized by a basal-disc-specific chitin synthase. Applying exogeneous chitinase abolished both WGA staining and Hydra attachment, indicating that WGA-positive components perform essential roles in adhesion. Our results therefore describe a glycan-dominated matrix, organized via a lectin-like protein (HvAb1), which is reinforced by chitin and enables reversible adhesion underwater. This establishes Hydra as a tractable model to better understand the principles of reversible adhesion underwater and, potentially, inform future bioinspired, sustainable adhesives.

zoology↗

bioRxiv2025

Examination of germline and somatic intercellular bridges in Hydra vulgaris reveals insights into the evolutionarily conserved mechanism of intercellular bridge formation

Incomplete cytokinesis results in the formation of stable intercellular bridges that have been extensively studied in bilaterians, where they play essential roles in cell-cell communication and coordination of differentiation. However, little is known about their structure and molecular composition in non-bilaterian animals. This study characterizes germline and somatic intercellular bridges in the cnidarian Hydra vulgaris, providing insights into their evolutionary origins and functional significance. We identified key conserved components, including KIF23, F-actin, and phosphotyrosine. Notably, we observed microtubule localization within Hydra ring canals, suggesting previously unrecognized functions for this cytoskeletal component in intercellular bridge formation. Bioinformatic analyses confirmed the conserved expression of Kif23 and suggested its role as a molecular marker for identifying ring canal-associated components. EdU incorporation during DNA replication demonstrated that cells connected by ring canals exhibit synchronized cell cycles, which may be critical for the coordination of division and differentiation. Our findings reveal that the molecular and structural features of intercellular bridges in Hydra are conserved across evolutionary lineages, highlighting their ancient origins and functional significance in cellular connectivity. The presence of synchronized cell cycles in ring canal-connected cells underscores their role in promoting coordinated cellular behaviors, processes fundamental to multicellular organization. This study provides new perspectives on the evolution of incomplete cytokinesis and establishes a framework for comparative investigations into the diversity and conservation of intercellular bridge mechanisms across metazoans.

cell biology↗

bioRxiv2023

A new look at the architecture and dynamics of the Hydra nerve net

The Hydra nervous system is the paradigm of a "simple nerve net". Nerve cells in Hydra, as in many cnidarian polyps, are organized in a nerve net extending throughout the body column. This nerve net is required for control of spontaneous behavior: elimination of nerve cells leads to polyps that do not move and are incapable of capturing and ingesting prey (Campbell, 1976). We have re-examined the structure of the Hydra nerve net by immunostaining fixed polyps with a novel antibody that stains all nerve cells in Hydra. Confocal imaging shows that there are two distinct nerve nets, one in the ectoderm and one in the endoderm, with the unexpected absence of nerve cells in the endoderm of the tentacles. The nerve nets in the ectoderm and endoderm do not contact each other. High-resolution TEM and serial block face SEM show that the nerve nets consist of bundles of parallel overlapping neurites. Results from transgenic lines show that neurite bundles include different neural circuits and hence that neurites in bundles require circuit-specific recognition. Nerve cell-specific innexins indicate that gap junctions can provide this specificity. The occurrence of bundles of neurites supports a model for continuous growth and differentiation of the nerve net by lateral addition of new nerve cells to the existing net. This model was confirmed by tracking newly differentiated nerve cells.

neuroscience↗

bioRxiv2022

New Hydra Genomes Reveal Conserved Principles of Hydrozoan Transcriptional Regulation

The epithelial and interstitial stem cells of the freshwater polyp Hydra are the best characterized stem cell systems in any cnidarian, providing valuable insight into cell type evolution and the origin of stemness in animals. However, little is known about the transcriptional regulatory mechanisms that determine how these stem cells are maintained and how they give rise to their diverse differentiated progeny. To address such questions, a thorough understanding of transcriptional regulation in Hydra is needed. To this end, we generated extensive new resources for characterizing transcriptional regulation in Hydra, including new genome assemblies for Hydra oligactis and the AEP strain of Hydra vulgaris, an updated whole-animal single-cell RNA-seq atlas, and genome-wide maps of chromatin interactions, chromatin accessibility, sequence conservation, and histone modifications. These data revealed the existence of large chromatin interaction domains in the Hydra genome that likely influence transcriptional regulation in a manner distinct from topologically associating domains in bilaterians. We also uncovered the transcriptomic profiles of two previously molecularly uncharacterized cell types, isorhiza-containing nematocytes and somatic gonad ectoderm. We identified novel candidate regulators of cell-type-specific transcription, several of which have likely been conserved at least since the divergence of Hydra and the jellyfish Clytia hemisphaerica over 200 million years ago. The resources generated in this study, which collectively represent the most comprehensive characterization of transcriptional regulation in a cnidarian to date, are accessible through a newly created genome portal, available at research.nhgri.nih.gov/HydraAEP/.

developmental biology↗

bioRxiv2022

An ancient role for the Hippo pathway in axis formation and morphogenesis

How did cells of early metazoan organisms first organize themselves to form a body axis? The canonical Wnt pathway has been shown to be sufficient for induction of axis in Cnidaria, a sister group to Bilateria, and is important in bilaterian axis formation. Here, we provide experimental evidence that in cnidarian Hydra the Hippo pathway regulates the formation of a new axis during budding upstream of the Wnt pathway. The target of Hippo pathway, the transcriptional co-activator YAP, inhibits the initiation of budding in Hydra, and is regulated by Hydra LATS. In addition, we show functions of Hippo pathway in regulation of actin organization and cell proliferation in Hydra. We hypothesize that Hippo pathway served as a link between continuous cell division, cell density and axis formation early in metazoan evolution.

developmental biology↗

bioRxiv2021

Mechanical stretch regulates macropinocytosis in Hydra vulgaris

Cells rely on a diverse array of engulfment processes to sense, exploit, and adapt to their environments. Macropinocytosis is a versatile example of such a process, allowing for the indiscriminate and rapid uptake of large volumes of fluid and membrane. Much of the molecular machinery essential for macropinocytosis has been well established. However, most of these studies relied on tissue culture models, leaving the regulation of this process within the context of organs and organisms unresolved. Here, we report that large-scale macropinocytosis occurs in the outer epithelial layer of the cnidarian Hydra vulgaris. Exploiting Hydras relatively simple body plan, we developed approaches to visualize macropinocytosis over extended periods of time in living tissue, revealing constitutive engulfment across the entire body axis. Using pharmacological perturbations, we establish a role for stretch-activated channels, including Piezo, and downstream calcium influx in inhibiting this process. Finally, we show that the direct application of planar stretch leads to calcium influx and a corresponding inhibition of macropinocytosis. Together, our approaches provide a platform for the mechanistic dissection of constitutive macropinocytosis in physiological contexts and reveal a role for macropinocytosis in responding to membrane tension.

cell biology↗