Ribosome biogenesis gene DEF/UTP25 is essential for liver homeostasis and regeneration

Digestive-organ-expansion-factor (Def) is a nucleolar factor. Depletion of Def causes hypoplastic digestive organs in zebrafish. Mechanistically, Def recruits cysteine proteinase Calpain3 (Capn3) to the nucleolus to cleave target proteins including p53 and Mpp10 during organogenesis. Here researchers demonstrate that Def is also essential for liver homeostasis and regeneration in mouse, a mammalian model. Their results reveal a novel feature of nucleolus, also called the ‘nucleus of a nucleus’, a subcellular organelle known for ribosome biogenesis.