Figure 2: WISH against isl1 (antisense 3′-untranslated region-probe; upper row), slc20a1a (middle row) and both probes combined (lower row) on wild-type zfl at 48 hpf.

48 hpf long-pec stage zfl in lateral (left column) and dorsal view (middle column; same fish; scale bar = 500 μm) in the top row are showing isl1 expression amongst other previous described regions also at most anterior regions of the proximal convoluted tubular (PCT; arrows). 25 μm transversal slices sections of the same fish are shown in the right column (scale bar = 150 μm). The orientation of sections is shown with red dashed lines in the corresponding whole mount images. The zfl show a clear isl1 staining in what has previously been described as the developing pancreatic region, and which might well be overlapping with an anterior region of the slc20a1a labeled PCT (black arrow heads). The overlap of isl1 and slc20a1a expression at this region is further supported by the fact that no additional stained area could be found there, when we used both in situ probes simultaneously for staining. Isl1 expression could not be detected in the developing cloaca or proctodeum region (not shown).