(A–D) dorsal view (A’–D’) view of the animal pole. At shield stage osr1 is expressed in the shield and germ ring of the embryo (A, A’). Maternal zygotic one eyed pinhead
(MZoep) mutants, which lack all Nodal signaling, show a complete loss of osr1 expression (B, B’). Mutants bonnie and clyde(bon) and schmalspur(sur), which have reduced Nodal signaling, show a reduction of osr1 expression (C, C’ and D, D’, respectively).