Brown and beige adipocytes expend chemical energy to produce heat and are 
therefore important in regulating body temperature and body weight. Brown 
adipocytes develop in discrete and relatively homogenous depots of brown adipose 
tissue, whereas beige adipocytes are induced to develop in white adipose tissue 
in response to certain stimuli - notably, exposure to cold. Fate-mapping 
analyses have identified progenitor populations that give rise to brown and 
beige fat cells, and have revealed unanticipated cell-lineage relationships 
between vascular smooth muscle cells and beige adipocytes, and between skeletal 
muscle cells and brown fat. In addition, non-adipocyte cells in adipose tissue, 
including neurons, blood vessel-associated cells and immune cells, have crucial 
roles in regulating the differentiation and function of brown and beige fat.