The study investigates the dynamics of adipogenesis in different fat depots during development, high-fat diet (HFD) feeding, and cold exposure using a novel inducible, permanent labeling system for mature adipocytes called the AdipoChaser mouse. Key findings include: 1. **Hypertrophy vs. Hyperplasia**: During HFD feeding, epididymal fat increases primarily through hypertrophy, while subcutaneous fat increases through both hypertrophy and hyperplasia. After prolonged HFD exposure, epididymal fat shows a high rate of adipogenesis, while subcutaneous fat maintains a low rate. 2. **Beige Adipocytes**: Cold exposure or β3 agonist treatment induces de novo adipogenesis in subcutaneous fat, leading to the formation of beige adipocytes. These beige adipocytes arise from de novo differentiation rather than transdifferentiation from existing white adipocytes. 3. **Epididymal Adipogenesis**: Cold exposure also induces widespread white adipocyte differentiation in epididymal fat, a process that is distinct from the browning effect seen in subcutaneous fat. This adipogenesis is rapid and occurs within a few days of cold exposure. 4. **Developmental Timing**: Gonadal fat develops postnatally, while subcutaneous fat develops between embryonic days 14 and 18. Adipocyte commitment and differentiation in subcutaneous fat occur earlier than in gonadal fat. 5. **Clinical Implications**: The variation in adipogenesis rates and dynamics between different fat depots highlights the importance of understanding depot-specific characteristics for therapeutic interventions targeting obesity and metabolic syndrome. The study provides insights into the complex physiology of adipose tissue and the mechanisms underlying adipogenesis, which have implications for the development of treatments for obesity and related metabolic disorders.The study investigates the dynamics of adipogenesis in different fat depots during development, high-fat diet (HFD) feeding, and cold exposure using a novel inducible, permanent labeling system for mature adipocytes called the AdipoChaser mouse. Key findings include: 1. **Hypertrophy vs. Hyperplasia**: During HFD feeding, epididymal fat increases primarily through hypertrophy, while subcutaneous fat increases through both hypertrophy and hyperplasia. After prolonged HFD exposure, epididymal fat shows a high rate of adipogenesis, while subcutaneous fat maintains a low rate. 2. **Beige Adipocytes**: Cold exposure or β3 agonist treatment induces de novo adipogenesis in subcutaneous fat, leading to the formation of beige adipocytes. These beige adipocytes arise from de novo differentiation rather than transdifferentiation from existing white adipocytes. 3. **Epididymal Adipogenesis**: Cold exposure also induces widespread white adipocyte differentiation in epididymal fat, a process that is distinct from the browning effect seen in subcutaneous fat. This adipogenesis is rapid and occurs within a few days of cold exposure. 4. **Developmental Timing**: Gonadal fat develops postnatally, while subcutaneous fat develops between embryonic days 14 and 18. Adipocyte commitment and differentiation in subcutaneous fat occur earlier than in gonadal fat. 5. **Clinical Implications**: The variation in adipogenesis rates and dynamics between different fat depots highlights the importance of understanding depot-specific characteristics for therapeutic interventions targeting obesity and metabolic syndrome. The study provides insights into the complex physiology of adipose tissue and the mechanisms underlying adipogenesis, which have implications for the development of treatments for obesity and related metabolic disorders.