Nodal flow and Pkd2 control Ablim1 expression at the node. (a) Ablim1 expression in a 4 somite Pkd2 mutant. (b) Ablim1 expression in a 5 somite iv mutant. (c) Ablim1 expression in a 5 somite wild type control embryo. In both iv mutants, which lack nodal flow and Pkd2 mutants, Ablim1 expression was not detected in the usual peri-nodal ring; a patchy expression across the floor of the node was seen in a significant proportion of embryos, in striking contrast to wild type control embryos (c).