Fig. 4. A distinct subpopulation responds to BMP2 and undergoes osteogenic differentiation. (A,B) Satellite cell-derived colonies obtained in EDL-fiber culture were exposed to BMP2 on days 2-4 (A) or days 7-9 (B). They were then subjected to staining for ALP. Scale bar: 20 µm. (C,D) Analysis of the ability to respond to BMP2 by satellite cell-descendants derived from EDL- (C) or soleus- (D) fiber cultures. Satellite cell-derived colonies were exposed to BMP2 on days 2-4 (BMP d2-4) or days 7-9 (BMP d7-9), or were cultured for the same periods in the absence of BMP2. Light blue indicates colonies that contain neither thick cells nor ALP-positive cells (ALP–; Thick–). Yellow indicates colonies that contain thick cells but no ALP-positive cells (ALP–; Thick cell+). Dark red indicates colonies that contain ALP-positive cells but no thick cells (ALP+; Thick cell–). Dark blue indicates colonies that contain both ALP-positive cells and thick cells (ALP+; Thick cell+). The numbers of colonies examined were 52-109 in control cultures without exposure to BMP2 and 107-199 in cultures exposed to BMP2.