Axolotls are uniquely able to resolve spinal cord injuries, but little is known about the mechanisms underlying spinal cord regeneration. We previously found that tail amputation leads to reactivation of a developmental-like program in spinal cord ependymal cells (Rodrigo Albors et al., 2015), characterized by a high-proliferation zone emerging 4 days post-amputation (Rost et al., 2016). What underlies this spatiotemporal pattern of cell proliferation, however, remained unknown. Here, we use modelling, tightly linked to experimental data, to demonstrate that this regenerative response is consistent with a signal that recruits ependymal cells during ~85 hours after amputation within ~830mm of the injury. We adapted FUCCI technology to axolotls (AxFUCCI) to visualize cell cycles in vivo. AxFUCCI axolotls confirmed the predicted appearance time and size of the injury-induced recruitment zone and revealed cell cycle synchrony between ependymal cells. Our modeling and imaging move us closer to understanding bona fide spinal cord regeneration.
Jupyter Notebook (http://jupyter.org/) containing the source code for all computations performed and referred to as Cura Costa et al., 2021 in this study can be found at https://doi.org/10.5281/zenodo.4557840
- Osvaldo Chara
- Osvaldo Chara
- Osvaldo Chara
- Emanuel Cura Costa
- Elly M Tanaka
- Leo Otsuki
- Aida Rodrigo Albors
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Animal experimentation: The licenses necessary for work with genetically modified organisms (GMOs) and for experiments specifically involving axolotls (Ambystoma mexicanum) were obtained from the relevant authorities and have been implemented at the IMP in accordance with applicable international, EU and national (Austrian) guidelines.The license for work with GMOs at safety levels 1 and 2 was approved by the GMO office of the Austrian authorities and was issued on 16/03/2017 with no end date (BMGF‐76110/0017‐ II/B/16c/2017).The axolotl research license numbers are GZ: 51072/2019/16 (valid 09/05/2019 - 28/02/2024) and GZ: MA58/665226/2019/21 (valid 24.02.2020 - 30.09.2024). These are approved by the City of Vienna, MA58.There is a dedicated veterinarian for the animal facility, as well as an animal welfare consultant. Animal facility inspections are performed yearly by the City of Vienna, MA58 and the animal licenses and animal husbandry conditions are updated in dialogue with animal welfare authorities.Axolotls (Ambystoma mexicanum) were raised in individual aquaria. Axolotl breedings were performed by the IMP animal facility. All experiments were performed in accordance with locally applicable ethics committee guidelines and within a framework agreed with the Magistrate of Vienna (Austria). Axolotls were anaesthetized with benzocaine (Sigma) diluted in tap water prior to amputation and/or imaging, to minimize suffering.
- Alejandro Sánchez Alvarado, Stowers Institute for Medical Research, United States
© 2021, Cura Costa et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
Axolotls are uniquely able to mobilize neural stem cells to regenerate all missing regions of the spinal cord. How a neural stem cell under homeostasis converts after injury to a highly regenerative cell remains unknown. Here, we show that during regeneration, axolotl neural stem cells repress neurogenic genes and reactivate a transcriptional program similar to embryonic neuroepithelial cells. This dedifferentiation includes the acquisition of rapid cell cycles, the switch from neurogenic to proliferative divisions, and the re-expression of planar cell polarity (PCP) pathway components. We show that PCP induction is essential to reorient mitotic spindles along the anterior-posterior axis of elongation, and orthogonal to the cell apical-basal axis. Disruption of this property results in premature neurogenesis and halts regeneration. Our findings reveal a key role for PCP in coordinating the morphogenesis of spinal cord outgrowth with the switch from a homeostatic to a regenerative stem cell that restores missing tissue.
In order to understand morphogenesis, it is necessary to know the material properties or forces shaping the living tissue. In spite of this need, very few in vivo measurements are currently available. Here, using the early Drosophila embryo as a model, we describe a novel cantilever-based technique which allows for the simultaneous quantification of applied force and tissue displacement in a living embryo. By analyzing data from a series of experiments in which embryonic epithelium is subjected to developmentally relevant perturbations, we conclude that the response to applied force is adiabatic and is dominated by elastic forces and geometric constraints, or system size effects. Crucially, computational modeling of the experimental data indicated that the apical surface of the epithelium must be softer than the basal surface, a result which we confirmed experimentally. Further, we used the combination of experimental data and comprehensive computational model to estimate the elastic modulus of the apical surface and set a lower bound on the elastic modulus of the basal surface. More generally, our investigations revealed important general features that we believe should be more widely addressed when quantitatively modeling tissue mechanics in any system. Specifically, different compartments of the same cell can have very different mechanical properties; when they do, they can contribute differently to different mechanical stimuli and cannot be merely averaged together. Additionally, tissue geometry can play a substantial role in mechanical response, and cannot be neglected.