Fig. 2. Nephric expression of sim1. (A) Dorsal view showing sim1 expression in the intermediate mesoderm. This is first evident at the two-somite stage. (B) Double in situ hybridization using sim1 and wt1 probes indicates that the posterior limit of wt1 expression coincides with the anterior limit of sim1 expression (arrow). (C) The anterior limit of sim1 expression lies at the level of somite four or five. Similar labeling experiments with pax2.1 (D) and pax8 (E) reveal that their anterior limit lies at the level of somite two. (F) sim1 continues to be expressed in the intermediate mesoderm and the ventrolateral portion of the somite throughout the segmentation period. (A,C,D,E) Dorsal views; (B) Lateral view; (F) Dorsolateral view. Anterior is towards the left in all panels. im, intermediate mesoderm; s, somite.