Extensive but irregular UB branching in <i>Gdnf−/−; Spry1−/−</i> and <i>Ret−/−; Spry1−/−</i> double mutant kidneys.

<p>(A–D) Newborn stage kidneys, all carrying the <i>Hoxb7/myrVenus</i> transgene to label the UB branches. Each panel shows a high magnification view of the kidney surface, revealing the shape and organization of branching UB tips; insets show the entire kidney in whole mount. Wild-type kidneys (A) have evenly spaced UB tips with a regular branching pattern, whereas <i>Gdnf−/−</i>;<i>Spry1−/−</i> (B) and <i>Ret−/−</i>;<i>Spry1−/−</i> (C) double mutant kidneys have highly irregular branching. <i>Spry1−/−</i> kidneys (D) have regularly branched, but swollen UB tips. (E–P) 3D volume rendering of E15.5 kidneys. (E–H) Whole kidneys from embryos of the indicated genotypes, carrying <i>Hoxb7/myrVenus</i>. (I–P) Higher power views of two representative surface regions of each genotype. The 3D images were generated from confocal Z-stacks, using Volocity (E–H) or ImageJ (I–P). The yellow dashed lines indicate an interpretation of the branching patterns. While most UB branches in the wild-type (I,M) and <i>Spry1−/−</i> (L,P) kidneys show a reiterative pattern of terminal bifurcation, with branches forming at right angles to their predecessors, most UB branches in the double mutants (J,K,N,O) fail to conform to this pattern, and instead display a variety of abnormal shapes and branching patterns.