Migration of apical and basolateral polarity proteins during podocyte differentiation.

Frozen kidney sections of newborn Wistar rat (P0) were stained using antibodies against the apical membrane protein Podocalyxin, the apical polarity protein Par3 and the basolateral polarity protein Scribble and were subjected to confocal laser microscopy. Since glomerular development is asynchronous, kidneys of newborn rats display various glomerular developmental stages. Each panel displays the expression pattern of the accordant proteins during glomerular development (from left to right): Developmental stages ranging from comma-shaped body (I), s-shaped body (II), capillary loop stage (III to IV), to a maturing glomerulus (V). (A) Whereas Par3 is expressed during comma-shaped body stage and localizes to the apical sited cell-cell junctions, expression of Podocalyxin starts during s-shaped body stage, when Par3 and the cell-cell contacts translocate along the lateral side of immature podocytes to basal. During this translocation the apical membrane area, marked by Podocalyxin, increases while the basolateral membrane area shrinks relatively. Arrows indicate translocation of Par3 from the apical cell-cell contacts in I to the developing foot processes in V. (B) Scribble localizes basal of Par3 at the cell-cell junctions and at the basolateral membrane during comma-shaped body stage (I) and translocates like Par3 during podocyte differentation to the developing foot processes in V. (C) While Podocalyxin and Par3 as well as Par3 and Scribble display an partial overlap of their localization (yellow in A and B), no overlap of Podocalyxin and Scribble can be detected indicating a localization to completely distinct membrane areas with Podocalyxin as an apical membrane marker and Scribble as a basolateral marker protein. Scale bars: 5 µm.