Fig. 1: Comparison of bone structure in young versus old axolotl and axolotl versus mouse.
From: The specialist in regeneration—the Axolotl—a suitable model to study bone healing?
a The upper hind limb samples of 6 cm, 13 cm and 25 cm snout-to-tailtip axolotl and 12 weeks-old mouse (Movat’s pentachrome staining). In young axolotls, the skeleton is cartilaginous, and with time it ossifies. Old axolotl femur is calcified all over the bone surface (yellow). In a, b: yellow - mineralized tissue, green - cartilage, light blue - connective tissue and red/orange is muscle. Scale bars 500 µm. b Femur epiphyseal ends of 6 cm (left), 13 cm (middle left), 25 cm (middle right) snout-to-tailtip axolotls and mouse tibia (right). Unlike mammals, amphibians do not have articular joints. The bone ends are cartilaginous and responsible for the length growth of the bone, analogous to the growth plate in the mouse. Scale bars 200 µm. c Axolotl epiphyses resemble the prenatal (E14.5) and early postnatal (P0) mouse bones. Movat’s pentachrome staining, or DAPI/EdU staining; scale bars 100 µm (left), 200 µm (right). d Safranin O/Light green staining of axolotl and mouse bones (cells are purple-brown, bone and soft tissue - green, cartilage - bright red). Left: bone marrow of an old axolotl. Note the huge fatty vacuoles (marked with * in a, b, d) and only few cells and not fully calcified bone cortices even in the old axolotls. Middle: bone marrow of 2 years-old mouse. Right: bone marrow of a young 12 weeks old mouse with only few fatty vacuoles. Scale bars 50 µm.
