Metabolites produced by agat+ cells support regeneration in the planarian Schmidtea mediterranea.

Planarians exhibit extraordinary regenerative abilities driven by pluripotent neoblasts, yet the roles of post-mitotic progenitor and differentiated cells in this process remain incompletely understood. Here, we investigate the function of agat⁺ cells, epidermal progenitors expressing members of the arginine:glycine amidinotransferase (agat) gene family, in the regeneration of Schmidtea mediterranea. Comprehensive analysis of all five planarian agat paralogs revealed that agat-1, -2, -3, and -4 are co-expressed in subepidermal populations enriched at wound sites, while agat-5 is minimally expressed. RNAi-mediated knockdown of agat-1 and agat-2 resulted in severe defects: agat-1 primarily disrupted tissue homeostasis, whereas agat-2 specifically impaired blastema formation and stem cell maintenance during regeneration. Transcriptional profiling of isolated agat⁺ cells demonstrated enrichment for metabolic and transport-related genes, including those involved in creatine and ornithine metabolism, as well as secretory pathway components. Functional assays showed that creatine supplementation partially rescued regeneration defects following agat-2 knockdown, implicating creatine and related metabolites as critical factors for regenerative success. These findings redefine agat⁺ cells as a heterogeneous, metabolically active, and potentially secretory population that supports regeneration beyond their canonical role as transitional progenitors. Our results highlight the importance of differentiated support cells and their metabolic outputs in tissue regeneration, providing new insight into the coordination between progenitor populations and stem cells during whole-body regeneration in planarians.