Fig. 3

tbx2a/b deficiency leads to a decrease in the size of the DL segment and a slight expansion in the PCT segment in the pronephros. Upper panel: At 28 ss, double whole mount in situ hybridization was used to label segmental domains in wild-type and tbx2a/b deficient embryos. Somites were labeled using smyhc1 (red) to detect length changes in adjacent pronephros segments (purple). Within proximal domains, MO knockdown of tbx2a, tbx2b, or tbx2a/b induced a 1-somite expansion in the slc20a1a-expressing PCT segment in morphant pronephros. This same expansion was also seen in fby^c144 mutants (tbx2b deficient) and fby^c144 mutants injected with tbx2a MO. Within distal domains, tbx2a/b deficient morphants and mutants exhibited a 1–2 somite reduction in the slc12a3-expressing DL segment at 24 hpf. The PST and DE segments, labeled by transcripts encoding trpm7 and slc12a1, respectively, exhibited a 1 somite posterior shift in tbx2a/b deficient embryos compared to wild-type embryos due to changes in the domain size of the PCT and DL segments. Representative wild-type and morphant results are based on somite counting of at least 20 embryos per marker. In fby^c144 embryos, segments showed consistent changes based on somite counting of at least 3 genotype-confirmed mutants per marker. Lower panel: Schematic summary of pronephros segment organization in wild-type and tbx2a/b deficient embryos. Abbreviations: PCT (proximal convoluted tubule), PST (proximal straight tubule), DE (distal early tubule), DL (distal late tubule) and MO (morpholino).