Non-canonical primary body axis segmentation through a multi-potent progenitor during axolotl tail regeneration
The ability of the axolotl to regenerate its tail represents a striking ability of vertebrate primary body axis regeneration, but how this process is regulated remains largely unknown. Current models of regeneration as seen in for example axolotl limb regeneration suggest a resident connective tissue population undergoes dedifferentiation after which developmental programs are re-deployed. In the context of tail regeneration this imply redeployment of somitogenesis, however previous work has suggested myomere are the earliest segmenting structures and are added in a non-linear fashion. Here we describe a resident progenitor in the axolotl tail which contributes to all regenerating paraxial mesodermal lineages. Moreover tail patterning as exemplified by vertebral segmentation is dependent on a somite independent non-canonical program. We find resident progenitors are in an inter-myomeric region and express a unique set of marker genes including Lfng, Scx, and Meox. Both during development and regeneration these cells contribute to myogenic, sclerogenic, and dermogenic lineages. While lineage contributions during regeneration closely recapitulate development, tissue patterning during regeneration follows a non-canonical somite independent program. In the absence of somites, there is no rostro-caudal polarity and resegmentation as a consequence is lost Moreover vertebrae are accurately re-established both after tail amputation as well as after vertebral extirpation. Finally, somitic mutant animals recover from vertebral malformations during regeneration, showing that even on a genetic level there are significant differences in tissue patterning programs during development and regeneration. Taken together these results show that even within a single organism multiple tissue specific modes of regeneration can exists: while limb regeneration is dependent on the dedifferentiation of connective tissue cells followed by the redeployment of developmental programs, tail regeneration is dependent on a resident progenitor cell population followed by the deployment of a patterning program which is distinct from canonical developmental programs.
Cardiac Regeneration, Newt
Since cardiac regeneration in vertebrates was first reported in the newt in 1974, the research field has expanded to teleosts (zebrafish) and mammals (mouse, and potentially human). In order to elucidate the principle of cardiac regeneration, comparative research among these vertebrates will be important. In the present study, we developed a cryo-injury procedure for the newt. We showed the gene expression profiles in cardiac regeneration induced by cryo-damage differed from the profiles induced by conventional ventricular amputation. Our results suggest that the cryo-injury method is suitable for comparing the process of cardiac regeneration in the newt with that in other animal models.
Marko Pende (Online)
Tissue-clearing and light-sheet imaging for in toto histological interrogation of organs and organisms
Tissue clearing in combination with light-sheet microscopy enabled scientists to observe regeneration, development, or the connectome in entire animals without the necessity of histological sectioning. However, the vast variety of different tissue clearing methods often ponders the question which protocol to use for an organ, animal, or animal developmental stage of interest. After mastering tissue clearing, the decision for the right imaging system introduces another level of difficulty. In this technical presentation we try to show the best tissue clearing approaches for different axolotl development stages raging from early embryo to 5cm animals. Further, we show different ways to image such tissue-cleared samples.
James Monaghan (Online)
Regeneration of the axolotl lung
Mammals have a limited capacity to repair their lung after injury. In contrast, we show here that axolotls are capable of lung regeneration after partial pneumonectomy. We show that injury induces an organ-wide proliferative response that supports regrowth of the missing lung tissue rather than generating a blastema. To identify epithelial cell populations involved in axolotl lung regeneration, we performed single-cell RNA-seq on uninjured lungs. We identified seven potential epithelial cell types in the axolotl lung, corresponding to most of the major cell types in the mammalian lung. We then used 12-plexed fluorescence in situ hybridization comprised of candidate cell type markers. This spatial analysis showed that the axolotl lung epithelium has a complex tissue architecture consisting of multiple specialized cell types.