Before they were fat: adipocyte progenitors.

Adipose tissue mass can expand throughout adult life. Therefore, proliferative adipocyte precursor cells must stand at the ready to respond to increased demand for energy storage. Recent provocative studies have identified discrete immature cell populations from which brown and white adipocytes are derived. This work not only brings fundamental insight into adipose tissue formation but also provides new tools to study how adipogenesis is regulated in pathological conditions such as obesity and diabetes.