Fig. 1

tbx2a/b transcripts are specifically expressed in the caudal domain of the renal progenitor field during nephrogenesis. (A) Schematic of zebrafish pronephros development. The intermediate mesoderm (IM) gives rise to the two-nephron pronephros, which is fully segmented by 24 hpf (28 ss): P (podocytes), N (neck), PCT (proximal convoluted tubule), PST (proximal straight tubule), DE (distal early tubule), CS (corpuscle of Stannius), DL (distal late tubule) and PD (pronephric duct). (B) Whole mount in situ hybridization shows that tbx2a and tbx2b transcripts are expressed in the distal region of the pronephros. At 14 ss, tbx2a transcripts can be detected in the distal region of the intermediate mesoderm while tbx2b transcripts are observed in a smaller distal domain. At 22 ss, tbx2b expression in the distal pronephros closely resembles tbx2a expression in this region. However, by 28 ss, tbx2a transcripts are most intensely expressed in the PD segment and trail off in the DL segment, while tbx2b transcripts are evident throughout the DL and more sparsely in the PD. (C) Flat-mount images of embryos co-stained with tbx2a and myoD, and tbx2b and myoD show that tbx2a is more widely expressed in the emergent distal pronephros than tbx2b at 14 ss. At 16 ss, tbx2b expression expands and begins to resemble tbx2a expression. (D) Fluorescent in situ hybridization shows that tbx2a and tbx2b are co-expressed in portions of the PD and DL at 28 ss. Specifically, tbx2a is expressed more intensely in the PD than tbx2b. In addition, tbx2b has a stronger expression in the DL, while tbx2a expression begins to taper off.