Fig. 5. Nodal expression after treatment with antagonists of Ca_i²⁺ asymmetry. Embryos received the indicated agent on the left or the right at HH3++/HH4 and Nodal expression was evaluated at HH8 or HH9- by using in situ hybridization. Images are dorsal views with anterior to the top, left (L) and right (R) are as indicated in A; arrows indicate expression. (A,B) Normal, left-sided Nodal expression in a DMSO-treated embryo having 3 somites (A) or 5 somites (B). (C) Bilateral Nodal expression in a 3-somite embryo that received left-sided Bapta-AM. (D) Normal Nodal expression in 4-somite embryo receiving right-sided Bapta-AM. (E) Loss of lateral Nodal expression in a 3-somite embryo receiving right-sided ionomycin (arrow); a faint signal is seen at the left node (arrowhead). (F) Six-somite embryo receiving left-sided ryanodine plus EGTA; Nodal expression is absent apart from a small amount to the left of the tailbud (arrowhead); compare with the 5-somite control embryo in B. (G) Loss of Nodal expression in a 4-somite embryo that received left-sided calmidizolium; note Nodal expression in the tailbud region (arrowhead).