Biology subjects

Hobmayer, B.

Publications and source records attributed to Hobmayer, B..

4 recordsLinked to original sources

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↗