Figure 2.

Expression of irx genes is highly regionalized in the developing pronephric kidney. (A–C) Expression patterns of irx1 (A), irx2 (B), and irx3 (C) in the pronephric kidneys of stage 35/36 Xenopus embryos as determined by whole-mount in situ hybridization. Lateral views of whole embryos (left panels; arrowheads indicate pronephric expression), enlargements of the pronephric region (middle panels), and color-coded schematic representations of the segment-restricted expression domains (right panels) are shown. Note the sharp boundaries that limit the expression domains of irx genes in the developing nephron. (D) Summary of the temporal expression profiles of irx genes during pronephric kidney development. The embryonic stages of X. laevis development are indicated. High and low levels of irx gene expression are illustrated with thick and thin lines, respectively. The embryonic expression patterns in early embryos are shown in Supplementary Figure 1.