Photomicrograph showing mCD24 expression in cells in colonies derived from transduced primate CFC using in situ labeling in agarose with anti-mCD24 followed by Streptavidin-conjugated alkaline phosphatase and development of the positive pink color reaction using Fast Red Substrate. In this photograph, colonies are counterstained blue-black with hematoxylin. Pink colonies are those that contain cells expressing the mCD24 transduced gene. In this low-magnification photomicrograph, 3 mCD24-positive pink colonies (P) and 2 of the several negative blue colonies (N) are indicated. No pink colonies were seen in any colony assays performed using progenitors that were not transduced (not shown). For actual visual scoring it is easier to count the total number of pink colonies in an agarose disk before counterstaining, where negative colonies show no color, and then score total colonies in the same disk after counterstaining.