Dynamic spatiotemporal expression changes during late somitogenesis precede the appearance of segment identities in the pronephros. Gene expression patterns of transcription factors in nephron progenitors in wild-type embryos at the 20, 22, 24, and 28 somite stage. Embryos are shown in lateral views with anterior to the left, and have been stained by whole-mount in situ hybridization to mark kidney gene expression (purple) and the somites with mhc (red). Black lines indicate areas of high gene expression, and numbers correspond to the somite position. The spatial distributions of hnf1ba, hnf4a, hnf1bb, emx1, and gata3 transcripts were unaltered between 20 and 28 somites of development, although note that the proximal boundary of the emx1 and gata3 domains at 20 somites changed since the 15 somite stage (compare with Fig. 1B). The expression domains of pou3f3a and pou3f3b were altered at 22 and 28 somites, the irx3b and grhl2a expression domains changed at 24 somites, and the etv5 domain was restricted at the 28 somite stage. The expression domain of mecom exhibited multiple alterations between 20 and 28 somites.
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