Effect of bone morphogenetic protein-4 (BMP-4) on adipocyte differentiation from mouse embryonic stem cells

Embryonic stem (ES) cells can differentiate spontaneously into various lineages in vitro. However, spontaneous commitment of ES cells to the adipocyte lineage is rare. In the present study, bone morphogenic protein-4 (BMP-4) is described as a factor inducing adipocyte differentiation from ES cells at a high rate. For this reason, ES-cell-derived embryoid bodies (EBs) in suspension cultures were exposed to different doses of BMP-4 for 5 days before they were plated onto gelatin-coated tissue culture plates. Moreover, the effect of serum-containing and serum-free media in three different combinations was assessed. Plated EBs, stained with Sudan Black and processed for transmission and scanning electron microscopy, were observed daily for adipocyte formation. Treatment with BMP-4 resulted in the appearance of adipocyte clusters in EBs' outgrowth, depending on the doses applied. Early in differentiation, many small fat droplets were observed in adipocytes, while later on they coalesced and formed a few large fat droplets. Adipocyte clusters had a fibrillar and vascular stroma, and each adipocyte was surrounded with a reticular external lamina. Furthermore, the appearance and development of adipocytes and their changes following 2-3 weeks of starvation mimicked live adipose tissue. In fact, understanding the biological activity of growth and differentiation factors is needed to regulate and direct stem cell differentiation to specific cell types in vitro.