Cells for blastema formation: Lessons from the annelid regenerative model.

Regeneration in many animals involves the formation of blastema, a mass of undifferentiated, proliferating cells. The origin of blastema cells is a key question in regenerative biology. Two major theories are: (1) the migration of lineage-restricted stem cells, supported by studies in salamanders and planaria, and (2) the dedifferentiation of somatic cells at the injury site, which has been observed in newts, mice, zebrafish, and crickets. Because different models support these theories, the generality of either mechanism is unclear. To address this, these theories should be investigated in a wider range of regenerative model animals. To this end, Fujita et al. (2024) studied the regenerative annelid Enchytraeus japonensis and discovered that soxC-expressing cells are crucial for blastema formation. In this review, we introduce an annelid model system for regeneration biology and the roles of soxC-expressing cells during blastema formation.