a–d, Sections from AxMLP-injected tails immunostained for BrdU/PAX7 (a, b) and BrdU/MEF2C (c, d) (refers to data in Fig. 2). Scale bars, 100 μm. e, Schematic illustration of the protein injection into axolotl limb. f, Quantification of BrdU+ cells in the limbs injected with PBS, flow-through or purified AxMLP (n = 4: biological replicates; centre values as median; points represent each sample). g–n, Transverse sections from purified AxMLP-injected (g–j) or flow-through-injected limbs (k–n). Scale bars: lower-magnification images, 200 μm; higher-magnification images, 50 μm. Sections were immunostained for BrdU (g, k), BrdU/myelin basic protein (MBP) (h, l), BrdU/PAX7 (i, m) and BrdU/GFP (j, n). GFP+ cells represent connective tissues in lateral plate mesoderm (LPM)-GFP transplanted axolotls. All molecular markers used except MBP had nuclear expression, and therefore allowed one-to-one colocalization of nuclear BrdU with nuclear staining of the marker. Therefore, we refer to the MBP data as ‘MBP-associated’. White boxes highlight the magnified images. Yellow circles indicate two bones in the lower limb. NS, not significant; *P < 0.05, **P < 0.005, ***P < 0.0005, ****P < 0.00005 with Student’s t-test. White arrowheads indicate marker+/BrdU+ cells.