Biology subjects

Tsiairis, C. D.

Publications and source records attributed to Tsiairis, C. D..

8 recordsLinked to original sources

bioRxiv2026

Optogenetic perturbations reveal temporal integration of Wnt signaling during pattern formation

The Wnt signaling pathway is a conserved regulator of tissue patterning and regeneration, yet how cells interpret dynamic Wnt inputs to generate robust developmental outcomes remains poorly understood. Here, we establish the first optogenetically activatable Hydra line, enabling precise temporal control of canonical Wnt signaling in vivo. Optogenetic stimulation induced dose-dependent patterning phenotypes whose rate of progression scaled with stimulation intensity. Transcriptomic analysis revealed that distinct combinations of signal intensity and duration converged onto shared transcriptional trajectories and could be described by an effective exposure metric that represents the cumulative signaling input. Functionally, Wnt activation rescued head regeneration under conditions that normally prevent organizer formation, and equivalent regenerative outcomes could be achieved through either strong, short-lived stimulation or weaker, prolonged activation. Together, our results indicate that Hydra tissues decode Wnt signaling through temporal integration of cumulative pathway activity, progressively accumulating transcriptional responses until patterning thresholds are reached. These findings establish a quantitative framework for understanding how dynamic morphogen signaling is translated into stable developmental decisions during regeneration.

developmental biology↗

bioRxiv2025

Rac1 inhibition slows down the segmentation clock and increases the somite size

The presomitic mesoderm (PSM) is a transient embryonic tissue patterned along the anterior-posterior (A/P) axis of vertebrates that periodically generates somites at its anterior end. This process, termed somitogenesis, is driven by waves of gene expression that travel from the posterior to the anterior end of the PSM under the contol of the segmentation clock, a molecular oscillator. Using a primary culture system, we performed a small-scale chemical screen targeting cellular mechanical properties and we identified Rac1, a small GTPase, as a key regulator. Inhibition of Rac1 markedly altered the periodicity of gene expression waves and disrupted somite spatial organization. Further analyses showed that Rac1 inhibition modified gene expression patterns, notably affecting markers of the Wnt and Notch pathways which are central regulators of segmentation. These findings reveal a previously unrecognized role for Rac1-mediated signaling in coordinating the mechanical and molecular aspects of segmentation dynamics.

developmental biology↗

bioRxiv2024

A transcription factor toggle switch determines differentiated epidermal cell identities in Hydra

In Hydra, a simple cnidarian model, epithelio-muscular cells play a crucial role in shaping and maintaining the body architecture. These cells are continuously renewed as undifferentiated cells from the bodys mid-region get displaced toward the extremities, replacing shed, differentiated cells and adopting specific identities. This ongoing differentiation, coupled with the maintenance of distinct anatomical regions, provides an ideal system to explore the relationship between cell type specification and axial patterning. However, the molecular mechanisms governing epithelial cell identity in Hydra remain largely unknown. In this study, we describe a double-negative feedback loop between the transcription factors Zic4 and Gata3 that functions as a toggle switch to control epidermal cell fate. Zic4 is activated by Wnt signaling from the mouth organizer and triggers battery cell specification in tentacles. In contrast, Gata3 promotes basal disk cell identity at the aboral end. Functional analyses demonstrate that Zic4 and Gata3 are mutually antagonistic; suppression of one leads to the dominance of the other, and vice versa, resulting in ectopic cell specification. Notably, simultaneous knockdown of both factors rescues the phenotype, indicating that it is the balance between these transcription factors, rather than their absolute levels, that dictates cell identity. This study highlights the mechanisms by which distinct cellular identities are established at Hydra body termini and reveals how cell fate decisions are coordinated with axial patterning.

developmental biology↗

bioRxiv2024

Mechanochemical Patterning Localizes the Organizer of a Luminal Epithelium

The spontaneous emergence of tissue patterns is often attributed to biochemical reaction-diffusion systems. In Hydra tissue regeneration, the formation of a Wnt signaling center serves as a well-known example of such a process. However, despite extensive research, a strictly biochemical mechanism for self-organization in Hydra remains elusive. In this study, we investigated mechanical stimuli and identified a positive feedback loop between Wnt signaling and tissue stretching. We developed a mathematical model of mechanochemical pattern formation in a closed elastic shell, representing regenerating Hydra epithelial spheroids. Our model explains how mechanical forces drive axis formation and predicts the organizers location under various perturbations, providing a more comprehensive understanding of the spatial dynamics involved. Validation by partially confining regenerating tissues showed that the organizer indeed forms in regions with the greatest stretching potential. This work highlights a novel mechanochemical mechanism for luminal epithelium patterning, suggesting that mechanical forces, in addition to biochemical signals, play a crucial role in tissue regeneration and axis specification. Our findings offer broader implications for the role of mechanical forces in tissue organization in various biological systems, opening new avenues for investigating mechanochemical feedback in development and regeneration.

developmental biology↗

bioRxiv2024

Progressive cell fate specification in morphallactic regeneration

Through regeneration various species replace lost parts of their body. This is achieved either by growth of new structures at the amputation side (epimorphosis), as is the case of axolotl limb regeneration, or through remodeling of the remaining tissue (morphallaxis), as happens in Hydra. Whereas work on epimorphic regeneration support a gradual proximal to distal establishment of cell identities, morphallactic regeneration is believed to rely on initial establishment of boundary conditions that organize the re-adjustment of the pattern. Performing single cell RNA sequencing during regeneration in Hydra, we revealed the sequence of cells transdifferentiation into the missing identities. We provide evidence that morphallaxis proceeds with progressive specification of cell fates, unifying its mechanism with the one found for epimorphosis.

developmental biology↗

bioRxiv2023

Open top multi sample dual view light sheet microscope for live imaging of large multicellular systems

Multicellular systems grow over the course of weeks from single cells to tissues or even full organisms composed of several thousands of cells, making live imaging of such samples challenging. To bridge these wide spatiotemporal scales, we present an open top dual view and dual illumination light sheet microscope dedicated for live imaging of large specimens at single cell resolution. The novel configuration of objectives together with a flexible and customizable multi-well mounting system combines dual view with high throughput multi-position imaging. We use the newly developed microscope to image a wide variety of samples and highlight its capabilities to gain quantitative single-cell information in large specimens such as mature intestinal organoids and gastruloids.

developmental biology↗

bioRxiv2020

Wnt3 expression as a readout of tissue stretching during Hydra regeneration

Mechanical forces shape cell fate decisions during development and regeneration in many systems. Epithelial lumen volume changes, for example, generate mechanical forces that can be perceived by the surrounding tissue and integrated into cell fate decisions. Similar behavior occurs in regenerating Hydra tissue spheroids, where periodic osmotically driven inflation and deflation cycles generate mechanical stimuli in the form of tissue stretching. Using this model, we investigate how such mechanical input guides the de novo formation of differentiated body parts. We show that the expression of the organizer-defining factor Wnt3 functions as a quantitative readout of cellular stretching and, when supplied externally, enables successful regeneration without mechanical stimulation. This finding represents a previously undescribed cellular mechanism for converting mechanical stimuli to a biochemical signaling readout and guiding cell fate transitions. It also elucidates the role of mechanical oscillations in Hydra regeneration, which long remained unclear. The presence the Wnt/mechanics interplay in Hydra and its relatives underscores the ancient evolutionary history of this crosstalk, possibly extending back to the first metazoans. Since Wnt signaling crosstalks with cellular mechanics in various developmental and disease contexts, it can also represent a conserved feature of this signaling pathway.

developmental biology↗

bioRxiv2020

Cellular Synchronisation through Unidirectional and Phase-Gated Signalling

Multiple natural and artificial oscillator systems achieve synchronisation when oscillators are coupled. The coupling mechanism, essentially the communication between oscillators, is often assumed to be continuous and bidirectional. However, the cells of the presomitic mesoderm synchronise their gene expression oscillations through Notch signalling, which is intermittent and directed from a ligand-presenting to a receptor-presenting cell. Motivated by this mode of communication we present a phase-gated and unidirectional coupling mechanism. We identify conditions under which it can successfully bring two or more oscillators to cycle in-phase. In the presomitic mesoderm we observed the oscillatory dynamics of two synchronizing cell populations and record one population halting its pace while the other keeps undisturbed, as would be predicted from our model. For the same system another important prediction, convergence to a specific range of phases upon synchronisation is also confirmed. Thus, the proposed mechanism accurately describes the coordinated oscillations of the presomitic mesoderm cells and provides an alternative framework for deciphering synchronisation.

systems biology↗