Appendage regeneration requires IMPDH2 and creates a sensitized environment for enzyme filament formation

Abstract

The regeneration of lost tissue requires biosynthesis of metabolites needed for cell proliferation and growth. Among these are the purine nucleotides ATP and GTP, which are required for diverse cellular processes including DNA synthesis, cytoskeletal assembly, and energy production. The abundance and balance of these purines is regulated by inosine monophosphate dehydrogenase 2 (IMPDH2), which catalyzes the committing step of GTP synthesis. IMPDH2 is typically expressed at high levels in proliferating cells and assembles into filaments that resist allosteric inhibition under conditions of high GTP demand. Here we asked whether IMPDH2 is required in the highly proliferative context of regeneration, and whether its assembly into filaments takes place in regenerating tissue. We find that inhibition of IMPDH2 leads to impaired tail regeneration and reduced cell proliferation in the tadpole Xenopus tropicalis. Upon treatment with IMPDH inhibitors, we find that both endogenous and fluorescent fusions of IMPDH2 robustly assemble into filaments throughout the tadpole tail, and that the regenerating tail creates a sensitized condition for filament formation. These findings clarify the role of purine biosynthesis in regeneration and reveal that IMPDH2 enzyme filament formation is a biologically relevant mechanism of regulation in vertebrate regeneration.