Fig. 1

sim1a expression is dynamic during nephrogenesis. (A) Schematics depict the IM and PM domains in a young zebrafish embryo. At 24 hpf, the zebrafish pronephros consists of two segmented nephrons as indicated by the colored regions. Corresponding numbers indicate the boundaries of each segment respective to the somites. (B) Illustrations denote the developmental time course of sim1a expression, which first appears within the IM (pax2a+ domain) at the 2 ss. Dark purple indicates strong expression, while light purple signifies weak expression. (C) Flat mounted embryos staged at young developmental time points were assayed by WISH for the kidney markers pax2a, sim1a, or mecom (purple). The somites and proximal renal progenitors were labeled by dlc or myod1 (red). Solid lines (purple and red) demarcate renal progenitors regions where high transcript expression was observed. The dotted line (purple) indicates a weak expression domain, with line color corresponding to the gene identity indicated in figure. (D) Embryos at older stages were analyzed by WISH for sim1a expression (purple). Embryo anterior is located to the left in all panels. Abbreviations: CS – corpuscles of Stannius; DE – distal early; DL – distal late; hpf – hours post fertilization; IM – intermediate mesoderm; N – neck; P – podocytes; PCT – proximal convoluted tubule; PD – pronephric duct; PM – paraxial mesoderm; PST – proximal straight tubule; ss – somite stage; WISH – whole mount in situ hybridization.