Practice question

Regenerative scaling requires coordination of growth and patterning to match body size. Notum-Wnt antagonistic balance achieves this: posterior muscle cells secrete Wnt ligands promoting proliferation of underlying neoblast progeny and posterior tail expansion, while anterior midline muscle secretes Notum deactivating Wnt locally limiting growth and allowing head differentiation. Negative feedback adjusts Wnt range ensuring proportional head-tail domains regardless of fragment size. Hedgehog modulates wnt expression but not size sensing, JAK-STAT influences stem cell maintenance and differentiation, Pax6 controls eye regeneration specifically. Thus Notum-Wnt ratio serves as scalable rheostat controlling both identity and organ size during regeneration.