From fragment to form: whole-body regeneration in a model urochordate

Tissue and organ regeneration are common among aquatic invertebrates, yet these taxa and their potential as model organisms remain underexplored. We present evidence of extensive regenerative capabilities in aquatic invertebrates, highlighting examples of whole-body regeneration (WBR), a peak form of regeneration, where entire organisms regenerate from minute body fragments. Among the many examples of WBR, we focus on botryllid ascidians, an intriguing group of invertebrate chordates that display chordate tissue complexity while demonstrating WBR from small fragments of blood vessels. Centering on WBR in the model species Botrylloides leachi, we outline shared characteristics of WBR across botryllid ascidians including the presence of circulating multipotent stem cells, systemic induction processes, and ensuing competition among regeneration sites, culminating in the restoration of a complete organism. This regeneration mode is distinct from those in mammals and humans. Further research may offer valuable insights into mechanisms by which tissue fragments reinstate new organisms.