Figure 6. Pet1 is expressed in the ureteric bud-derived tissues during kidney development.

(a–f) Radioactive ISH performed on coronal section of 10.5 dpc (a–b), 11.5 dpc (c–d) and 12.5 dpc (e–f) Pet1₂₁₀-Cre/ROSA26YFP (a–d) and wild-type (e–f) embryos. Results show presence of Pet1 mRNA expression in the nephric duct (arrowheads) already at 10.5 dpc (a), mirroring YFP reporter expression (b). At 11.5 dpc both Pet1 and YFP expression is highlighted in the two forming ureteric buds (c–d, arrowheads), while Pet1 but not the reporter expression is detectable in 12.5 dpc wild-type embryos (e–f), confirming the specificity of Pet1 expression in the developing kidney. (g–j’) X-gal staining performed on whole-mount 9.5 dpc (g, g’), 10.5 dpc (h, h’), 13.5 dpc (i, i’) Pet1₂₁₀-Cre/ROSA26R mouse embryos and on coronal sections of a P1 Pet1₂₁₀-Cre/ROSA26YFP mouse kidney (j, j’). Staining performed at different stages of development traces Pet1-expressing cell lineage during ureteric bud formation as highlighted in boxed regions shown in the higher magnification images (g’, h’, i’). Cre-mediated recombination has already occurred at 9.5 dpc in some scattered cells in the caudal nephric duct (g’). X-gal stained cells become more numerous at 10.5 dpc (h’) and depict the ureteric bud branching at 13.5 dpc (i’). At P1, X-gal staining highlights that Cre expressing cells have contributed to the formation of the collecting duct system (j) and ureter (j’). (k–n’) Brightfield (k, k’) and fluorescence images of whole-mount 13.5 dpc Pet1₂₁₀-Cre/ROSA26YFP kidneys immunostained for YFP (l, l’) and calbindin-D28K (m, m’). Merge images (n, n’) show colocalization of Cre recombinase activity and the specific ureteric bud-derivative marker calb-D28K during kidney development. Scale bar: 1.2 mm (i), 600 µm (h), 500 µm (e, f, k–n), 400 µm (a–d, g, j), 200 µm (h’–i’), 100 µm (j’, k’–n’), 80 µm (g’).