Secreted inhibitors drive the loss of regeneration competence in Xenopus limbs.

Can Aztekin,Benjamin David Simons,Jerome Jullien,John Gurdon,John Marioni,Tom W. Hiscock

doi:10.1242/dev.199158

Abstract

ABSTRACTAbsence of a specialized wound epidermis is hypothesized to block limb regeneration in higher vertebrates. However, the factors preventing its formation in regeneration-incompetent animals are poorly understood. To characterize the endogenous molecular and cellular regulators of specialized wound epidermis formation in Xenopus laevis tadpoles, and the loss of their regeneration competency during development, we used single-cell transcriptomics and ex vivo regenerating limb cultures. Transcriptomic analysis revealed that the specialized wound epidermis is not a novel cell state, but a re-deployment of the apical-ectodermal-ridge (AER) programme underlying limb development. Enrichment of secreted inhibitory factors, including Noggin, a morphogen expressed in developing cartilage/bone progenitor cells, are identified as key inhibitors of AER cell formation in regeneration-incompetent tadpoles. These factors can be overridden by Fgf10, which operates upstream of Noggin and blocks chondrogenesis. These results indicate that manipulation of the extracellular environment and/or chondrogenesis may provide a strategy to restore regeneration potential in higher vertebrates.

Highlights

Amphibian limb regeneration relies on a specialized wound epidermis that forms on the amputation plane and has been characterized primarily
Quantitative features of AER cell formation are associated with regeneration outcome We focused on the specialized wound epidermis, or AEC, that was suggested to be analogous to the AER
As BMP4 boosts chondrogenesis (Fig. S12E), which can, in turn, lead to Noggin expression, these results suggest that fine-tuning of BMP agonist and antagonists levels in the growing limb are key for AER cell formation

Summary

Introduction

Some marker genes associated with AEC (e.g. Fgf and Fn1) were seen only in the basal layers of AEC tissue, suggesting there is cellular heterogeneity within the AEC (Christensen and Tassava, 2000; Tsai et al, 2020; Yokoyama et al, 2000). It remains largely unclear which cell types within AEC tissue are crucial for regeneration, which transcriptional and functional properties are associated with a mature AEC and regeneration, and why the AEC cannot form or maturate in some instances and/or species

Methods

Results

Conclusion