Regulators of adipocyte precursor cells.

Lean and adipose tissue growth are two of the most important targets for manipulation in commercial livestock. Adipose tissue growth occurs by both hyperplasia and hypertrophy. The processes involved in adipocyte hypertrophy are relatively well understood but much less is known about adipocyte hyperplasia. The mature adipocyte has little capacity for cell division and the hyperplastic capacity of adipose tissue resides in a population of fibroblast-like adipocyte precursor cells. The origin of these cells and the processes involved in their commitment to the adipocyte lineage is not known. Growth factors, in particular the bone morphogenetic proteins (BMP), are likely to be involved in regulating commitment to the adipocyte lineage. In vitro studies have shown that once committed to the adipocyte lineage, the proliferation and differentiation of, adipocyte precursor cells is regulated by a number of different growth factors. A number of these growth factors are expressed in adipocyte precursor cells in vitro and may have an autocrine-paracrine role. Others, such as epidermal growth factor (EGF), are more likely to have an endocrine role. The precise role that each growth factor plays in regulating adipocyte development in vivo is poorly understood. The chick is a useful experimental system with which to study the precise function of growth factors in adipocyte development.