Fig. 6

Increased RA levels promote the proximalization of the nephron but are not sufficient to rescue PST formation in sim1a morphants. (A) Wild-type embryos or (B) sim1a morphants were treated with either a 1×10⁷ M DMSO control, a low dose of RA (1×10⁸ M; denoted as+RA), or with a higher RA concentration of 1×10⁷ M (denoted as ++ RA). Both the DMSO control and ++ RA dose were given from the 90% epi to 5–7 ss while the+RA dose was applied from 90% epi to the 15 ss. Changes to nephron segmentation after the addition of RA was visualized by WISH in embryos at 24 hpf. The expression patterns of segment specific transcripts (purple) and smyhc1 transcripts, which marks the somites (red), are shown. Black lines with corresponding somite numbers were used to further illustrate segment domains. Embryo anterior is located to the left. (C) Schematic delineating the effects of low (+) and high (++) RA concentrations on nephron segmentation in wild-type embryos and sim1a morphants at 24 hpf. Nephron segments are represented by colored bars in relation to their corresponding somite numbers. Regions with lower transcript expression are indicated by stripes. Abbreviations: CS – corpuscles of Stannius; DE – distal early; DL – distal late; epi – epiboly; hpf – hours post fertilization; PCT – proximal convoluted tubule; PST – proximal straight tubule; RA – retinoic acid (+ RA – low; ++ RA – high dose); ss – somite stage; WISH – whole mount in situ hybridization.