Biology subjects

Tsissios, G.

Publications and source records attributed to Tsissios, G..

6 recordsLinked to original sources

bioRxiv2024

Species-specific oxygen sensing governs the initiation of vertebrate limb regeneration

Why mammals cannot regenerate limbs, unlike amphibians, presents a longstanding puzzle in biology. We show that exposing ex vivo amputated embryonic mouse limbs to subatmospheric oxygen environment, or stabilizing oxygen-sensitive HIF1A enables not only rapid wound healing, but alters cellular mechanics, and reshapes the histone landscape to prime regenerative fates. Conversely, regenerative Xenopus tadpole limbs display low oxygen-sensing capacity, robust wound healing, a regenerative histone landscape, and glycolytic programs even under high oxygen. This reduced oxygen-sensing capacity, in stark contrast to mammals, associates with decreased HIF1A-regulating gene expressions. Our findings thus uncover species-specific oxygen sensing as a unifying mechanism for limb regeneration initiation across vertebrates, reveal how aquatic subatmospheric habitats may enhance regenerative capabilities, and identify targetable barriers to unlock latent limb regenerative programs in adult mammals.

developmental biology↗

bioRxiv2024

Specialized signaling centers direct cell fate and spatial organization in a limb organoid model

Specialized signaling centers orchestrate robust development and regeneration. Limb morphogenesis, for instance, requires interactions between the mesoderm and the signaling center apical-ectodermal ridge (AER), whose properties and role in cell fate decisions have remained challenging to dissect. To tackle this, we developed mouse embryonic stem cells (mESCs)-based heterogeneous cultures and a limb organoid model, termed budoids, comprising cells with AER, surface ectoderm, and mesoderm properties. mESCs were first induced into heterogeneous cultures that self-organized into domes in 2D. Aggregating these cultures resulted in formation of limb bud-like structures in 3D, exhibiting chondrogenesis-based symmetry breaking and elongation. Using our organoids and quantitative in situ expression profiling, we uncovered that AER-like cells support nearby limb mesoderm and fibroblast identities while enhancing tissue polarization that permits distant cartilage formation. Together, our findings provide a powerful model to study aspects of limb morphogenesis, and reveal the ability of signaling center AER cells to concurrently modulate cell fate and spatial organization.

developmental biology↗

bioRxiv2024

Spotiflow: accurate and efficient spot detection for imaging-based spatial transcriptomics with stereographic flow regression

Identifying spot-like structures in large and noisy microscopy images is a crucial step to produce high quality results in various life-science applications. Imaging-based spatial transcriptomics (iST) methods, in particular, critically depend on the precise detection of millions of transcripts in images with low signal-to-noise ratio. Despite advances in computer vision that have revolutionized many biological imaging tasks, currently adopted spot detection techniques are mostly still based on classical signal processing methods that often lack robustness to changing imaging conditions and thus require tedious manual tuning per dataset. In this work, we introduce Spotiflow, a deep learning method that achieves subpixel-accurate localizations by formulating the spot detection task as a multi-scale heatmap and stereographic flow regression problem. Spotiflow can be used for 2D images and 3D volumetric stacks and can be trained to generalize across different imaging conditions, tissue types and chemical preparations, while being substantially more time- and memory-efficient than existing methods. We show the efficacy of Spotiflow via extensive quantitative experiments on a variety of diverse datasets and demonstrate that the enhanced accuracy of SO_SCPLOWPOTIFLOWC_SCPLOW leads to meaningful improvements in the biological insights obtained from iST and live imaging experiments. Spotiflow is available as an easy-to-use Python library as well as a napari plugin at https://github.com/weigertlab/spotiflow.

bioinformatics↗

bioRxiv2023

Macrophages modulate fibrosis during newt lens regeneration

Previous studies indicated that macrophages play a role during lens regeneration in newts, but their function has not been tested experimentally. Here we generated a transgenic newt reporter line in which macrophages can be visualized in vivo. Using this new tool, we analyzed the location of macrophages during lens regeneration. We uncovered early gene expression changes using bulk RNAseq in two newt species, Notophthalmus viridescens and Pleurodeles waltl. Next, we used clodronate liposomes to deplete macrophages, which inhibited lens regeneration in both newt species. Macrophage depletion induced the formation of scar-like tissue, an increased and sustained inflammatory response, an early decrease in iris pigment epithelial cell (iPEC) proliferation and a late increase in apoptosis. Some of these phenotypes persisted for at least 100 days and could be rescued by exogenous FGF2. Re-injury alleviated the effects of macrophage depletion and re-started the regeneration process. Together, our findings highlight the importance of macrophages in facilitating a pro-regenerative environment in the newt eye, helping to resolve fibrosis, modulating the overall inflammatory landscape and maintaining the proper balance of early proliferation and late apoptosis.

developmental biology↗

bioRxiv2023

Multi-species atlas resolves an axolotl limb development and regeneration paradox

Humans and other tetrapods are considered to require apical-ectodermal-ridge, AER, cells for limb development, and AER-like cells are suggested to be re-formed to initiate limb regeneration. Paradoxically, the presence of AER in the axolotl, the primary regeneration model organism, remains controversial. Here, by leveraging a single-cell transcriptomics-based multi-species atlas, composed of axolotl, human, mouse, chicken, and frog cells, we first established that axolotls contain cells with AER characteristics. Surprisingly, further analyses and spatial transcriptomics revealed that axolotl limbs do not fully re-form AER cells during regeneration. Moreover, the axolotl mesoderm displays part of the AER machinery, revealing a novel program for limb (re)growth. These results clarify the debate about the axolotl AER and the extent to which the limb developmental program is recapitulated during regeneration.

developmental biology↗

bioRxiv2022

Regenerative hallmarks of aging: Insights through the lens of Pleurodeles waltl

BackgroundAging and regeneration are heavily linked processes. While it is generally accepted that regenerative capacity declines with age, some vertebrates, such as newts, can bypass the deleterious effects of aging and successfully regenerate a lens throughout their lifetime. ResultsHere, we used Optical Coherence Tomography (OCT) to monitor the lens regeneration process of larvae, juvenile, and adult newts. While all three life stages were able to regenerate a lens through transdifferentiation of the dorsal iris pigment epithelial cells (iPECs), an age-related decline in the kinetics of the regeneration process was observed. Consistent with these findings, iPECs from older animals exhibited a delay in cell cycle re-entry. Furthermore, it was observed that clearance of the extracellular matrix (ECM) was delayed in older organisms. ConclusionsCollectively, our results suggest that although lens regeneration capacity does not decline throughout the lifespan of newts, the intrinsic and extrinsic cellular changes caused by aging alter the kinetics of this process. By understanding how aging affects lens regeneration in newts, we can gain important insights for restoring the age-related regeneration decline observed in most vertebrates.

developmental biology↗