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Fig. 4 Expression analysis of pkd2. (A) RT-PCR of pkd2 at early developmental time-points shows presence of maternal pkd2 prior to mid-blastula transition at 1K stage. gapdh was used to control for variations in total RNA for each cDNA library. Maternal contribution of pkd2 RNA cannot be detected by in situ hybridization. (B-E) Lateral views of pkd2 expression patterns in wild-type (B,D) and MZoep (C,E) embryos; anterior is up. Expression of pkd2 is first noticeable at dome stage, where pkd2 expression marks the dorsal side of the embryo (arrowhead in B) and continues to be expressed in all dorsal marginal cells by 40% epiboly (D). pkd2 expression is in mesendodermal tissue as expression is lost in MZoep embryos (C,E). (F,J) pkd2 RNA is detected at the shield in gastrulating embryos, as well as in the dorsal forerunner cells (DFCs, arrowhead in F and J; F anterior view, dorsal to the right; J is a higher magnification dorsal view focusing on the DFCs). (G,K) At tailbud stage, pkd2 is detected in a circular patch of cells that will soon form Kupffer′s vesicle (arrowhead in G and K; G lateral view, anterior is up, dorsal to the left; K is a higher magnification posterior view of region in G denoted by the arrowhead). (H,I,L) Dorsal view of 8-somite (H) and 36-hpf (I) embryos and cross-section view of an 8-somite embryo (L). Faint pkd2 expression highlighting the pronephric collecting ducts is marked with arrows and the more intensely stained floorplate in the midline is marked with arrowheads.