Effects of FN fragments on the clonogenic capacity of human hematopoietic progenitor cells. (A) Schematic representation of FN molecules and FN fragments. FN is made up of a series of repeats termed Type I, II, and III. Regions of FN with proved cell-binding activity are shown as the RGD-containing CBD, the nonintegrin-dependent HBD, and the LDV-containing CS1 region (CS1). The portions adhere to VLA4 (▪) and VLA5 (▧) are also indicated. (B) The human CD34⁺ cells were incubated with 0.5 nmol/mL of FN or each FN fragment in serum-free IMDM at 37°C for 1 hour and subsequently cultured in methylcellulose media at 3.0 × 10²/mL to assess their clonogenic capacity. BSA was used as a control protein. The data are shown as mean ± SD of duplicate cultures. Statistically significant differences from a control (before incubation) value are indicated by one (P < .05) or two (P < .01) asterisks. Similar results were obtained in three independent experiments. (▨), BFU-E; (▪), CFU-GM.