. 2019 Sep 20;8:e48507. doi: 10.7554/eLife.48507

Table 1. Salient features of forelimb development between axolotl, Xenopus, chicken and mouse.

Feature	Axolotl	Xenopus	Chicken	Mouse	References
Autopod skeletal differentiation	Preaxial dominance¹	Postaxial dominance¹	Postaxial dominance¹	Postaxial dominance¹	¹ Shubin and Alberch, 1986
Location of ZPA domain	Posterior. Excluded from autopod^1,*	Posterior. Extends into autopod²	Posterior. Extends into autopod³	Posterior. Extends into autopod⁴	¹ Torok et al., 1999 ² Endo et al., 1997 ³ Riddle et al., 1993 ⁴ Echelard et al., 1993 * This study
Contribution of ZPA cells to posterior digit(s)	Yes (DiI labeling)^*	?	Yes (DiI labeling)¹ No (GFP grafting)²	Yes (Genetic labeling)³	¹ Towers et al., 2008 ² Towers et al., 2011 ³ Harfe et al., 2004 * This study
Shh-signaling during limb development	Key mediator of anterior-posterior patterning¹	Key mediator of proximal-distal and anterior-posterior patterning²	Key mediator of anterior-posterior patterning³	Key mediator of anterior-posterior patterning^{4, 5}	¹Stopper and Wagner, 2007 ²Stopper et al., 2016 ³ Ros et al., 2003 ⁴ Chiang et al., 1996 ⁵ Chiang et al., 2001
Morphological AER	No¹	Transient²	Yes³	Yes⁴	¹ Tank et al., 1977 ² Tarin and Sturdee, 1971 ³ Saunders, 1948 ⁴ Wanek et al., 1989
Molecular AER	No^*	Yes	Yes	Yes	* This study
Location of AER-specific Fgfs (4,8,9,17)	Mesenchyme^*	AER¹	AER^{2, 3, 4}	AER^{2, 5, 6, 7, 8, 9}	¹ Christen and Slack, 1997 ² Mahmood et al., 1995 ³ Duprez et al., 1996 ⁴ Havens et al., 2006 ⁵ Ohuchi et al., 1994 ⁶ Crossley and Martin, 1995 ⁷ Niswander and Martin, 1992 ⁸ Sun et al., 2002 ⁹ Sun et al., 2000 * This study
Location of Fgf receptors	FgfR1-4 expressed exclusively in the mesenchyme^*	?	FgfR1IIIc, FgfR2IIIb, FgfR3IIIb expressed in the ectoderm and FgfR1IIIb, FgfR2IIIc, FgfR3IIIb/c and FgfR4 expressed in the mesenchyme^{1, 2}	FgfR1IIIb and FgfR2IIIb expressed in the ectoderm and FgfR1IIIc, FgfR2IIIc, FgfR3c and FgfR4c expressed in the mesenchyme^{3, 4, 5}	¹ Havens et al., 2006 ² Sheeba et al., 2010 ³ Min et al., 1998 ⁴ MacArthur et al., 1995 ⁵ Ornitz and Itoh, 2015 * This study
Fgf-signaling during limb development	Controls cell proliferation and limb size^*	?	Regulates proximodistal patterning, cell survival and cellular differentiation^{1, 2, 3,4}	Regulates proximodistal patterning, cell survival and cellular differentiation^{5, 6}	¹ Saunders, 1948 ² Summerbell, 1974 ³ Janners and Searls, 1971 ⁴ Dennis Summerbell, 1977 ⁵ Sun et al., 2002 ⁶ Mariani et al., 2008 * This study
Positive regulation of Gremlin1 by Fgf-signaling in the limb	Yes^*	?	No¹	No²	¹ Merino et al., 1999 ² Verheyden and Sun, 2008 * This study
Positive regulation of Shh-signaling by Fgf-signaling in the limb	No^*	?	Yes¹	Yes²	¹ Crossley et al., 1996 ² Lewandoski et al., 2000 * This study
Positive regulation of Fgf-signaling by Shh-signaling in the limb	Yes^*	?	Yes¹	Yes²	¹ Laufer et al., 1994 ² Harfe et al., 2004 * This study
Limb regeneration	Regenerates complete limb through adulthood^{1, 2, 3}	Regenerates complete limb through larval stage 53⁴	Does not regenerate⁵	Does not regenerate. *Regenerates digit tip⁶	¹ Young et al., 1983a ² Young et al., 1983b ³ Monaghan et al., 2014 ⁴ Dent, 1962 ⁵ Muneoka and Sassoon, 1992 ⁶ Borgens, 1982