The Role of C/EBP Genes in Adipocyte Differentiation

One of the central problems facing higher animals is that cells require a continuous source of energy; however, it is impractical for organisms to meet this need by supplying a constant external source of calories. Two specialized tissues, brown and white adipose tissues, have evolved to meet the ongoing requirement for energy. White adipose tissue is able to store excess calories in the form of triacylglycerol. When cells require energy, such as during periods of fasting, these needs are largely met by fatty acids and glycerol formed from lipolysis of stored triacylglycerol. Brown adipose tissues use stored triacylglycerols to maintain body temperature. In particular, these cells convert energy from fatty acid metabolism to heat through the action of uncoupling protein 1 (UCP1), a mitochondrial protein found only in brown adipose tissue. Brown adipocytes contain less triacylglycerol and many more mitochondria than white adipocytes, resulting in their characteristic color. Humans and rats develop brown adipose tissue depots prenatally, and although these depots largely disappear in humans during childhood, some brown adipocytes likely remain interspersed in white adipose tissue throughout adulthood.