Fig. 1

mecom transcripts mark an early caudal domain of the renal progenitors, and the mecom expression domain is dynamic during nephrogenesis. (A) Schematic depictions of zebrafish pronephros at 24 hpf, shown in lateral view. Enlargement represents segmental organization of the nephron at 24 hpf. Abbreviations: G (glomerulus), N (neck), PCT (proximal convoluted tubule), PST (proximal straight tubule), DE (distal early), CS (corpuscle of Stannius), DL (distal late), PD (pronephric duct), and C (cloaca). (B) At the 2 and 3 somite stages, the renal progenitor field was labeled by pax2a (purple) and forming somites were marked by dlc (red). Onset of mecom expression in renal progenitors could be detected at the 3 somite stage, in a caudal domain exclusive to the dlc-expressing rostral domain. Inset shows non-overlapping expression territory of dlc (red) and mecom (purple) at 3 somites in the renal progenitor field. (C) Expression of mecom (purple) and myod1 (red) at various time points between 6 and 14 somite stages in wild types. At 14 somites, the expression domains of solute transporters slc4a4a and slc12a3 indicate premature patterning of the pronephros proximal versus distal segment regions. (D) Upper panel: genomic structure of zebrafish mecom202 (dark purple, bottom) and mecom201 (evi1) (light purple, top). The mecom202-52and mecom202-32 riboprobes (orange filled lines) were designed to distinguish mecom202 and mecom201 transcripts by targeting the 52 and 32 region exclusively present in mecom202 transcripts. Lower panels: in 24 hpf wild type embryos, WISH using a full-length mecom202 probe and mecom202-specific probes showed that mecom expression was restricted to the DL and PD regions of the pronephros.