Biology subjects

Tursch, A.

Publications and source records attributed to Tursch, A..

6 recordsLinked to original sources

bioRxiv2024

Tsa1 is the dominant peroxide scavenger and a source of H2O2-dependent GSSG production in yeast

Hydrogen peroxide (H2O2) is an important biological molecule, functioning both as a second messenger in cell signaling and, especially at higher concentrations, as a cause of cell damage. Cells harbor multiple enzymes that have peroxide reducing activity in vitro. However, the contribution of each of these enzymes towards peroxide scavenging in vivo is less clear. Therefore, to directly investigate in vivo peroxide scavenging, we used the genetically encoded peroxide sensors, roGFP2-Tsa2{Delta}CR and HyPer7, to systematically screen the peroxide scavenging capacity of yeast thiol and heme peroxidase mutants. We show that the 2-Cys peroxiredoxin Tsa1 alone is responsible for almost all exogenous H2O2 and tert-butyl hydroperoxide scavenging. The two catalases and cytochrome c peroxidase only produce observable scavenging defects at higher H2O2 concentrations when these three heme peroxidases are deleted in combination. We also analyzed the reduction of Tsa1 in vitro, revealing that the enzyme is efficiently reduced by thioredoxin 1 with a rate constant of 2.8x106 M-1s-1. When thioredoxins are oxidized, Tsa1 can become an important source of H2 O2 -dependent cytosolic glutathione disulfide production in yeast. Our findings clarify the importance of the various thiol and heme peroxidases for peroxide removal and suggest that most thiol peroxidases have alternative or specialized functions in specific subcellular compartments.

biochemistry↗

bioRxiv2023

Spatio-temporal Coordination of Active Deformation Forces and Wnt / Hippo-Yap Signaling in Hydra Regeneration

Ample evidence suggests that Wnt signaling and tissue deformation are key determinants for pattern formation in animals. The coordination of these biochemical and biomechanical spatio-temporal asymmetries is often unknown or controversial. We investigated this relationship by studying regeneration in the freshwater polyp Hydra. In both reaggregates of dissociated cells and tissue regenerates, we found significant tissue contraction waves and upregulation of Wnt signaling. Applying a simple mechanical model to the mode analysis of the active deformations, we quantitatively defined the phase reversal of size change and axial deformation in those oscillations as the time point of "biomechanical" symmetry breaking. Moreover, overexpression and inhibition of canonical Wnt signaling modulated the timing of this biomechanical symmetry breaking. A direct comparison with the RNAseq data indicates that the biomechanical symmetry breaking occurs only after the upregulation of canonical Wnt signaling. Further data suggest that biochemical signaling and biomechanical active deformation synergistically stabilize the body axis and hence the following head structure formation by Hippo-Yap signaling. The symmetry breaking mechanism identified here in Hydra most likely represents a patterning module that is evolutionary conserved from early metazoan to bilaterian animals.

biophysics↗

bioRxiv2021

How Dickkopf molecules and Wnt/beta-catenin interplay to self-organise the Hydra body axis

The antagonistic interplay between canonical Wnt signalling and Dickkopf (Dkk) proteins is fundamental to tissue organisation, including stem cell differentiation and body-axis formation. Disruptions in this interaction are linked to various human diseases, yet the mechanisms enabling robust body-axis formation through {beta}-catenin/Wnt-Dkk interactions remain unclear. A key model system for Wnt-driven pattern formation is the pre-bilaterian organism Hydra, where two ancestral Dkk proteins interact with Wnt signalling to self-organise the body axis. While Hydra patterning has been extensively studied using the activator-inhibitor framework, a model integrating experimentally identified molecules has been lacking. Here, we introduce a mathematical model that incorporates both Dkks and their experimentally observed interactions with Wnt signalling. Numerical and analytical studies show that this network alone is sufficient to drive de novo body-axis formation across a broad parameter range. Our mutual inhibition model provides a biologically grounded realization of the general local-activation/long-range-inhibition (LALI) principle of de novo pattern formation, offering a mechanistic explanation for the observed Dkk and Wnt expression patterns under various conditions. Unlike previous models, it is directly grounded in experimental data, links injury response to pattern formation, and remains robust against perturbations. Author SummaryHow organisms form and regenerate complex body structures is a fundamental question in biology. In the freshwater animal Hydra, which can regenerate its entire body from a small tissue fragment, a molecular signalling system involving Wnt proteins and their inhibitors, the Dickkopf (Dkk) family, plays a central role in organising the body axis. While these molecules are known to interact, their exact roles and how they collectively shape large-scale patterns have remained unclear--especially since their activity does not fully align with established pattern formation models. In this study, we present a new mathematical model that captures the observed interactions between Wnt and two Dkk molecules in Hydra. We show that a mechanism based on mutual inhibition--rather than the traditional interplay between activator and inhibitor molecules--can explain the emergence of a stable body axis and the results of various perturbation experiments. Our work offers new insights into the design principles of biological pattern formation and emphasizes the importance of exploring alternative mechanisms beyond classical theories.

developmental biology↗

bioRxiv2021

β-Catenin and canonical Wnts control two separate pattern formation systems in Hydra: Insights from mathematical modelling

The formation of body axes and apical termini is crucial for animal development. In Hydra, nuclear {beta}-catenin and Wnt3 play key roles and were previously thought to be part of a single mechanism for axis and head formation. This study challenges this view by combining mathematical modeling with experimental data. We show that {beta}-catenin and Wnt3 patterning in Hydra operate at two different scales, requiring distinct inhibitory mechanisms. {beta}-catenin, possibly interacting with other Wnts, co-ordinates axis formation, whereas Wnt3 is involved in small-scale head patterning. A double-loop reaction-diffusion model was developed, demonstrating the ability to describe patterns with divergent shapes, which single-loop models could not achieve. The previously proposed threshold mechanism for Wnt3 expression based on {beta}-catenin prepatterns could not explain the data. Our results suggest a more complex patterning mechanism in other animals, where axis and head formation may not be controlled by a single process.

developmental biology↗

bioRxiv2020

MAPK signaling links the injury response to Wnt-regulated patterning in Hydra regeneration

Hydra has a long history as an informative model to study pattern formation and regeneration. Wnt signaling is a critical component of Hydra patterning that must be activated during regeneration, but it is largely unknown how the injury stimulus ultimately leads to this activation. In a proteomic screen we previously identified mitogen protein kinases (MAPKs) among the earliest injury response factors in Hydra regeneration, making them attractive candidates to transmit injury-response signals to the initial steps of patterning, which in Hydra includes Wnt signaling. Our data demonstrate that three MAPKs, p38, c-Jun N-terminal kinases (JNKs), and extracellular signal-regulated kinases (ERK), are essential to initiate regeneration in Hydra. This activation occurs in response to an injury signal, which consists of calcium and reactive oxygen species (ROS) signaling. Phosphorylated MAPKs exhibit cross-talk with a mutual antagonism between the ERK1/2 pathway and the stress induced MAPKs. The activation of these MAPK pathways, as well as the induction of apoptosis, occurs in all injuries regardless of the position of the wound. MAPK phosphorylation is required for the transcriptional activation of position independent Wnt3 and Wnt9/10c ligands. In summary, our data show that the activation of MAPKs is an essential component of the wound response which transmits the injury signal to induce the transcriptional activation of Wnt ligands, which are essential for patterning the regenerating tissue. Given the high level of evolutionary conservation of MAPKs and Wnts in the injury response, this likely represents a deeply conserved pathway in animals.

developmental biology↗

bioRxiv2017

Genetic knockdown and knockout approaches in Hydra

Hydra is a member of the Cnidaria, an ancient phylum at the base of metazoan evolution and sister group to all bilaterian animals. The regeneration capacity of Hydra, mediated by its stem cell systems is unparalleled in the animal kingdom. The recent sequencing of the Hydra genome and that of other cnidarians has drawn new attention to this well-known model organism. In spite of this, the establishment of methods to manipulate gene expression in Hydra have remained a major challenge. Here we report a CRISPR-Cas9 based targeted mutation approach as well as an optimized, reproducible strategy for the delivery of siRNAs. Both approaches are based on a refined electroporation protocol for adult Hydra polyps. We demonstrate that these strategies provide reliable genetic interference with target gene expression, facilitating functional studies and genome editing in Hydra.

developmental biology↗