The putative stem cell markers K15 and α6 integrin, which have been previously reported to be expressed in the murine HF bulge region at high levels [29, 30], were confirmed to be strongly expressed in both bulge cells and basal cells of the HF outer root sheath (Fig. 1A, 1B, 1D, 1E). This evidence concerns the gene KRT15 and hydrops fetalis.