The proximal tubule, protein uptake, and the riddle of the segments

The proximal tubule is divided anatomically into 3 distinct segments-S1 to S3-on the basis of differences in cellular ultrastructure, but the functional processes that define and shape these remain elusive. In a new study, Christensen used 3-dimensional nephron reconstruction, electron microscopy, and antibody staining to precisely map protein uptake to the structure of the proximal tubule. They reported striking axial patterns in endocytosis along the segments, which showed substantial plasticity in disease states.