Fig. 2. Regeneration of new branching epithelia from E11.5 ureteric bud stalks. (A,B) New branching tree generated from an isolated E11.5 stalk surrounded by fresh mesenchyme, stained with (A) anti-calbindin-D_28K and (B) the stalk marker DBA. Comparison of the images reveals that at least some of the new tips are DBA negative (arrowheads). (C) Another example, stained for Wnt11 by in situ hybridization; the new tips have acquired Wnt11 expression. (D-F) Generation of a new ureteric bud tree from the `wrong end' of the ureteric bud. (D) Low-power view of a `double-ended' kidney formed by branching from the cut end of the ureteric bud. (E,F) Higher-power view of the `wrong end' tree, stained with anti-calbindin-D_28K (E) and DBA (F): a significant number of tips (outlined in F) have greatly reduced DBA expression compared with stalk (arrowhead). (G) These stalk-derived tips (Reg) express the tip marker Wnt11 by RT-PCR at levels similar to those in whole kidneys (kid), whereas the stalks not allowed to generate new tips (Slk) do not express it at detectable levels. Scale bars: 100 µm.