Fig1C(left). from [doi:10.1038/35071095] Nature 2001 410(6830): 825-30, Episkopou V; Arkell R; Timmons PM; Walsh JJ; Andrew RL; Swan D, Induction of the mammalian node requires Arkadia function in the extraembryonic lineages. Copyright 2001 [PMID:11298452]