Biology subjects

Salvenmoser, W.

Publications and source records attributed to Salvenmoser, W..

9 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↗

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

Local endoreduplication of the host is a conserved process during Phytomyxea-host interaction

Endoreduplication is a modified cell cycle in which cells duplicate their DNA without subsequent mitosis. This process is common in plants and can also be found in other organisms like algae and animals. Biotrophic plant pathogens have been shown to induce endoreduplication in their host to gain space and/or nutrients. Phytomyxea (divided into the Plasmodiophorida, the Phagomyxida, and the Marinomyxa clade) are obligate biotrophic parasites of plants, diatoms, brown algae, and oomycetes. Here, we tested if phytomyxids induce local endoreduplication in two distant hosts (plants and brown algae). By combining fluorescent in situ hybridisation (FISH) coupled with nuclear area measurements and flow cytometry, we confirmed that endoreduplication is induced by Plasmodiophora brassicae (Plasmodiophorida) in infected plants and demonstrate this process in combination with Maullinia ectocarpii and Maullinia braseltonii (Phagomyxida) in brown algae. We identified molecular signatures of endoreduplication in RNA-seq datasets of P. brassicae-infected Brassica oleraceae and M. ectocarpii-infected Ectocarpus siliculosus. Cell cycle switch proteins (CCS52A1 and B in plants and CCS52 in algae) as well as the protein kinase WEE1 (in plants) were identified as genes potentially important for the phytomyxean-induced switch from the mitotic cell cycle to the endocycle. Their expression pattern changed in infected plants and brown algae accordingly. In this study we expand the knowledge on Phytomyxea-host interactions by showing that induced endoreduplication in the host is a conserved feature in phytomyxid infections. The induction of this cellular mechanism by phytomyxid parasites in phylogenetically distant hosts further points at a fundamental importance of endoreduplication in these biotrophic interactions.

microbiology↗

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

Phagocytosis underpins the biotrophic lifestyle of intracellular parasites in the class Phytomyxea (Rhizaria)

Phagocytosis is a complex multi-gene trait of eukaryotes and allegedly one of the very defining features of this group. Although well documented for free-living unicellular eukaryotes and in specific cellular types of animals, data on phagocytosis in intracellular biotrophic parasites are scant. Indeed, the definition of intracellular biotrophy as complete reliance of a parasite on a living host, with which it constantly negotiates for the exchange of nutrients, is at odd with the consumption of particulate matter suggested by phagocytosis. Phytomyxea are intracellular biotrophic parasites infecting a broad group of hosts, ranging from plants to stramenopiles. They belong to the clade Rhizaria, where phagotrophy (i.e., phagocytosis as main mode to acquire nutrients) is the main mode of nutrition. The exact mode of nutrition of the biotrophic phytomyxea, including the agriculturally impactful phytomyxid Plasmodiophora brassicae, is still unresolved; despite investigations and the availability of molecular data. For other Phytomyxea, observations are patchy and molecular data altogether lacking. Here, using available genomic and transcriptomic data for Phytomyxea and the de novo sequenced transcriptome of the brown algae parasite Maullinia ectocarpii, we investigate the likelihood that the genetic machinery underpinning phagotrophy is conserved within the clade. We further document intracellular phagocytosis in P. brassicae and M. ectocarpii by transmission electron microscopy and fluorescent in situ hybridization. Our investigations confirm that molecular signatures underpinning phagocytosis exist in Phytomyxea and hint at a smaller subset of genes used for intracellular phagocytosis, which is similar between the two parasites. Microscopic evidence confirms the existence of intracellular phagocytosis, which seems to coexist with the manipulation of host physiology typical of biotrophic interactions. In both phytomyxid parasites investigated intracellular phagocytosis has adapted to the intracellular environment and seemingly targets specific organelles. Our findings shed light on the feeding behaviour of Phytomyxea, providing new molecular data for the class; and suggest a paramount and previously unrecognised role for phagocytosis in biotrophic interactions between host and parasite.

microbiology↗

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↗

bioRxiv2020

Extensive nuclear gyration and pervasive non-genic transcription during primordial germ cell development in zebrafish

Primordial germ cells (PGCs) are the precursors of germ cells, which migrate to the genital ridge during early development. Relatively little is known about PGCs after their migration. We studied this post-migratory stage using microscopy and sequencing techniques, and found that many PGC-specific genes, including genes known to induce PGC fate in the mouse, are only activated several days after migration. At this same timepoint, PGC nuclei become extremely gyrated, displaying general opening of chromatin and high levels of transcription. This is accompanied by changes in nuage morphology, expression of large loci, named PERLs, enriched for retro-transposons and piRNAs, and a rise in piRNA biogenesis signatures. Interestingly, no nuclear Piwi protein could be detected at any timepoint, indicating that the zebrafish piRNA pathway is fully cytoplasmic. Our data show that the post-migratory stage of zebrafish PGCs holds many cues to both germ cell fate establishment and piRNA pathway activation.

developmental biology↗

bioRxiv2019

Zebrafish Gpr161 contributes to basal hedgehog repression in a tissue-specific manner

Hedgehog (Hh) ligands act as morphogens to direct patterning and proliferation during embryonic development. Protein kinase A (PKA) is a central negative regulator of Hh signalling, and in the absence of Hh ligands, PKA activity prevents inappropriate expression of Hh target genes. The Gs- coupled receptor Gpr161 contributes to the basal Hh repression machinery by activating PKA, although the extent of this contribution is unclear. Here we show that loss of Gpr161 in zebrafish leads to constitutive activation of low-, but not high-level Hh target gene expression in the neural tube. In contrast, in the myotome, both high- and low-level Hh signalling is constitutively activated in the absence of Gpr161 function. Our results suggest that the relative contribution of Gpr161 to basal repression of Hh signalling is tissue-specific. Distinct combinations of G-protein-coupled receptors may allow the fine-tuning of PKA activity to ensure the appropriate sensitivity to Hh across different tissues.

cell biology↗

bioRxiv2018

Tdrd6a regulates the aggregation of Buc into functional subcellular compartments that drive germ cell specification

In recent years, it has become clear that phase separation represents an important class of subcellular compartmentalization. However, relatively little is known about how the formation or disassembly of such compartments is regulated. In zebrafish, the Balbiani body (Bb) and the germ plasm (Gp) are phase-separated structures essential for germ cell specification and home to many germ cell-specific mRNAs and proteins. Throughout development, these structures range from a single large aggregate (Bb), to a dispersed state and back to relatively large assemblies (Gp). Formation of the Bb requires Bucky ball (Buc), a protein with prion-like properties. We found that the multi-tudor domain-containing protein Tdrd6a interacts directly with Buc, affecting its mobility and aggregation properties. Importantly, lack of this regulatory interaction leads to significant defects in germ cell development. Our work presents a new mechanism for how prion-like protein-aggregations can be regulated and highlights the biological relevance of such regulatory events.

molecular biology↗