Figure 1F. Copyright: Reprinted with permission from Elsevier from [doi:10.1016/j.ydbio.2007.08.023] Dev Biol 311: 124-35, Nam JS; Park E; Turcotte TJ; Palencia S; Zhan X; Lee J; Yun K; Funk WD; Yoon JK, "Mouse R-spondin2 is required for apical ectodermal ridge maintenance in the hindlimb." Copyright 2007 [PMID:17904116]