The Molecular and Cellular Choreography of Appendage Regeneration Elly M. Tanaka  Cell  Volume 165, Issue 7, Pages 1598-1608 (June 2016) DOI: 10.1016/j.cell.2016.05.038 Copyright © 2016 Elsevier Inc. Terms and Conditions

Figure 1 Principles of Limb Regeneration Revealed by Classical Grafting Experiments (A) Grafting of a left limb blastema onto a right stump yield two “supernumerary limbs” (Iten and Bryant, 1975). Blue and red represent limb tissue with anterior and posterior identity, respectively. (B) Generation of a circular limb then amputation shows that the regenerate always regenerates distal elements from the level of amputation (Butler, 1955) (adapted from Nacu and Tanaka, 2011). Cell 2016 165, 1598-1608DOI: (10.1016/j.cell.2016.05.038) Copyright © 2016 Elsevier Inc. Terms and Conditions

Figure 2 Molecular Dissection of the Supernumerary Limb Phenomenon (A) In the “accesory limb model,” nerve is re-routed to anterior wound surface, which generates an “anterior blastema” that survives only for 19 days (left). Limb regeneration at the ectopic site is only completed if a piece of posterior limb tissue (red) is grafted to the anterior wound site (right) (Endo et al., 2004). (B) Provision of SHH to anterior blastemas or FGF8 to posterior blastemas is sufficient for completion of limb regeneration (Nacu et al, 2016). (C) Molecular circuitry in the regenerating limb blastema established by 12 days of regeneration. Posterior SHH maintains anterior FGF8 expression and vice versa (adapted from Nacu et al 2016). (D) The FGF8-SHH crosstalk is induced at three sites after left-to-right blastema transplantation (as in Figure 1A), leading to supernumerary limb formation. Cell 2016 165, 1598-1608DOI: (10.1016/j.cell.2016.05.038) Copyright © 2016 Elsevier Inc. Terms and Conditions

Figure 3 The Events of Limb Regeneration (A) Connective tissue cells in the mature limb have different determination states along the anterior-posterior and the proximal-distal axis. (B) After limb amputation, the wound epidermis releases MARCKS-Like Protein (MLP), which induces initiation of proliferation. (C) In growing nerves and macrophages release factors such as Neurgulin, NAG, FGF, and BMPs that sustain proliferation. A number of the nerve factors act in a relay to wound epidermis (blue highlight). (D) Blastema cells start to express developmental factors appropriate for their origin. Upper arm cells express MEIS, anterior cells express FGF8, and posterior cells express SHH. FGF8-SHH crosstalk further sustains growth. (E) As the blastema grows, cells diversify along the proximal-distal axis reflected by HOXA protein expression. Cell 2016 165, 1598-1608DOI: (10.1016/j.cell.2016.05.038) Copyright © 2016 Elsevier Inc. Terms and Conditions