Metanephrogenic mesenchyme-to-epithelium transition induces profound expression changes of ion channels

The expression patterns of plasma membrane transporters that specify the ep ithelial cell type are acquired with ontogeny. To study this process during metanephrogenic mesenchyme-to-epithelium transition, branching ureteric bu ds with their adjacent mesenchymal blastema (mouse embryonic day E14) were dissected and explanted on a collagen matrix. In culture, induced mesenchym al cells condensed, aggregated, and converted to the comma- and S-shaped bo dy. During in vitro condensation and aggregation, transcription factor Pax- 2 protein was downregulated while the epithelial markers E-cadherin and bet a-catenin proteins were upregulated. In addition, Wilms' tumor suppressor p rotein WT-1 was detectable upon condensation and downregulated in the S sta ge, where expression persisted in the long arm of the S. Patch-clamp, whole cell conductance (G, in nS/10 pF) of preepithelial condensed mesenchymal c ells (n = 7) was compared with that of tubular proximal S-shaped-body epith elium (n = 6). Both stages expressed E-cadherin and WT-1 mRNA, as demonstra ted by single-cell RT-PCR, testifying further to the epithelial as well as the nephrogenic commitment of the recorded cells. Mesenchymal cells exhibit ed whole cell currents (G = 6.7 +/- 1.3) with reversal potentials (V-rev, i n mV) near equilibrium potential for Cl- (E-Cl) (V-rev = -40 +/- 7) suggest ive of a high fractional Cl- conductance. Currents of the S-shaped-body cel ls (G = 4.0 +/- 1.1), in sharp contrast, had a V-rev at E-K (V-rev = -82 +/ - 6) indicating a high fractional K+ conductance. Further, analysis of K+-s elective whole cell tail currents and single-channel recording revealed a c hange in K+ channel expression. Also, Kir6.1 K+ channel mRNA and protein we re downregulated between both stages, whereas K(v)LQT K+ channel mRNA was a bundant throughout. In conclusion, metanephrogenic mesenchyme-to-epithelium transition is accompanied by a profound reorganization of plasma membrane ion channel conductance.