Figure 1

EGFP expression is limited to the capping mesenchyme and to early stage nephrons after birth, and demonstrates an abrupt change in morphology of the cap. GFP is expressed in the nephron progenitor mesenchyme of transgenic mice at birth and at lower levels in newly induce nephrons. The GFP signal in the mesenchyme at birth (P0) surrounds the branch tips of the ureteric bud which are unlabeled. The pattern changes very little until post-natal day 3 (P3) when the crescent-shaped mesenchyme begins to be replaced by renal vesicles, ovoid structures with central cavities (arrows). The images are 2 micron thick optical sections taken by a laser scanning microscope on a plane parallel to the tangent of the kidney surface through the cortical nephrogenic zone. The gain was increased at P3 to allow visualization of the reduced levels of GFP expression. The intensities between panels cannot be directly compared.