Figure 5

Expression domains of selected molecular marker genes validates the pronephric segmentation model. Whole-mount in situ hybridizations of stage 35/36 Xenopus embryos were performed. Lateral views of whole embryos (left panels), enlargements of the pronephric region (middle panels), and color-coded schematic representations of the segment-restricted expression domains (right panels) are shown. (a) cldn8: intermediate tubule (IT)2. Note that the expression levels are low. Arrowheads indicate the proximal and distal boundaries of the cldn8 expression domain. (b,d) cldn14 and cldn16: intermediate tubule, distal tubule (DT)1. (d) cldn19: nephrostomes (arrowheads), intermediate tubule. (e) clcnk: intermediate tubule, distal tubule, connecting tubule. Note that the dotted staining pattern localizes to cells of the epidermis. The localization of the clcnk expression domains has previously been reported [22] and is shown here for comparative purposes. (f) kcnj1: IT1, distal tubule, connecting tubule. The arrowhead indicates the location of IT2, which fails to express kcnj1. (g) calb1: connecting tubule. The arrowhead indicates the proximal boundary of the expression domain. Expression is highest in the most distal parts of the connecting tubule.