Organs and donor derived GFP⁺ hematopoietic cells can be visualized directly through the skin in the axolotl. (A) The underside of a wild-type white larval axolotl. The internal organs can be seen clearly through the skin. (B) The head of an irradiated white adult axolotl 1 month after HCT. The iris of the eyes (arrows) are autofluorescent but the nodes are regions of highly concentrated GFP⁺ donor-derived cells. (C) GFP channel with lighting to visualize GFP⁺ cells and non-GFP vasculature. Two GFP⁺ blood cells (white arrowheads) are flowing through vasculature in the tail of a transplanted axolotl in this frame. The orange is white light diffracting off of non-GFP tissues. (D) The foot of a transplanted axolotl with a patch of GFP⁺ HSPC-derived cells in the skin. Dashed line indicates a previous amputation site (transverse cut) and the section used for E. Dense recruitment of donor-derived cells suggests the potential involvement of blood cells in limb regeneration. (E) DIC image (×20) of the foot sectioned in D. Superior aspect of the inferior portion of the foot. Blue, DAPI staining of cell nuclei; green, donor-derived GFP⁺ cells. Scale bar: 100 µm. (F) Dissecting microscope view of static donor-derived cells in the skin.