Positional information modulates transient regeneration-activated cell states during vertebrate appendage regeneration.

Injury is a common occurrence in the life of most if not all organisms. Because injury and the extent of damage inflicted are not predictable events, pre-existing tissues must somehow determine how much tissue needs to be restored. It has been known for over a century that amputation position along a proximal-distal (P/D) axis determines the regeneration speed of amputated limbs in regeneration-competent animals1. Yet, it is not clear how an injured limb conveys positional information during regeneration to faithfully restore pre-existing morphologies and functions. Here, we profiled millimetric caudal fins regenerating proximal and distal amputations in the African killifish (Nothobranchius furzeri). We report position-specific, differential modulation of the spatial distribution, duration, and magnitude of proliferation, and the possibility to predict blastema sizes. Regenerating fins profiled by single cell RNA sequencing identified a Transient Regeneration-Activated Cell State (TRACS) enriched in extracellular matrix (ECM) components and modifiers that is proportionally amplified to match a given amputation position. We located this transient cell state to the basal epidermis by gene expression and confocal microscopy, and propose a role for these cells in transducing positional information to the regeneration blastema. Understanding the temporal deployment of regenerative cell states may hold the key to set up a successful regeneration event in organisms with limited regenerative abilities such as humans. Regenerating or homeostasis cells from caudal fins or dorsal fins were isolated by FACS according to live/nucleated signal and analyzed using scRNA-seq