Early developmental Hes1-creER+cell-derived marrow stromal cells behave as skeletal progenitor cells.A, Colony-forming unit fibroblast (CFU-F) assay of Hes1-creER; R26RtdTomato at P21, pulsed at E10.5 (top), E12.5 (middle), and E14.5 (bottom). Scale bar: 5 mm. B, Percentage of tdTomato+ colonies among total CFU-Fs. n = 4 (Hes1-E12.5), n = 5 (Hes1-E12.5), n = 3 (Hes1-E14.5) mice. ∗p < 0.05, ∗∗p < 0.01. Two-tailed, One-way ANOVA followed by Tukey’s post-hoc test. Data are presented as mean ± SD. MB, Methylene blue staining.