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Fig. S6 Transcription factor domain alterations in irx3b morphants correspond to changes in segment boundaries. A: Gene expression patterns of transcription factors in nephron progenitors in wild-type embryos and irx3b morpholino (MO) -injected animals at the 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. In irx3b morphants, the domains of hnf1ba, hnf1g, irx3b, mecom, emx1, and gata3 were unchanged, while the expression of hnf4a was expanded slightly and the rostral boundary of pou3f3a and pou3f3b were shifted distally by one somite. In addition, the pou3f3a domain was expanded to somite 14. B: The domain of transcription factor gene expression in wild-type and irx3b morphant embryos correlates closely to the segment pattern. (Foreground) Summary of transcription factor expression domains (represented by black bars) are schematized in the nephrons at the 28 somite stages (Note: wild-type schema is repeated from Fig. 3 for easy comparison). (Background) Nephron segment identities form adjacent to particular somites (demarcated by numbered columns, top), and each segment region is color-coded to envisage a comparison between the transcription factor expression domains and the nephron segments. Segment color codes are N, green; PCT, orange; PST, yellow; DE, light blue; DL, dark blue; and PD, gray.