The emergence of adipocytes.

In mammals, the adipose organ is composed of white adipocytes (primary site in energy storage) and of brown adipocytes (specialized in thermogenesis). Adipocytes arise from mesenchymal stem cells (MSCs) by a sequential pathway of differentiation. MSCs develop either from ectoderm or mesoderm and commit into different undifferentiated precursors, which upon the expression of key transcription factors enter a differentiation program to acquire their specific functions. When triggered by appropriate developmental cues, MSCs become committed to the adipocyte lineage. White adipocytes differentiate from various types of vascular cell types, probably located within the white adipose tissue itself. Brown adipocytes arise from myogenic precursors. The differentiation between white adipocyte and brown adipocyte lineages occurs in the earliest steps of the fetal development, and both phenotypes are acquired independently. A better knowledge of these differentiation pathways allows new therapeutic strategies for reconstruction of damaged conjunctive tissues and for the control or prevention of risks associated with obesity in humans.