Kidney Proximal Tubule Cells Originate from Approximately Four Progenitor Cells and Make Distinct Patches in Mouse Aggregation Chimeras

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Abstract
Giant lysosomal granules of bgJ/bgJ mutant mice were used as a marker to investigate the histological composition of kidney proximal tubule cells. Embryos of the bgJ/bgJ genotype and those of the +/+ genotype were aggregated, and lysosomes of their proximal tubule cells were histochemically stained with the β‐glucuronidase activity. Tubules composed of bgJ/bgJ‐type epithelial cells alone, tubules composed of +/+‐type epithelial cells alone and tubules containing both types of epithelial cells were observed in cross sections. When the long straight portion of proximal tubules was reconstructed from serial sections, most of the tubules were of the mixed type, and distinct patches of bgJ/bgJ‐type or +/+‐type epithelial cells were detectable. These patches appeared to extend to the longitudinal rather than the circumferential direction. This suggests the clonal proliferation followed the mixing of embryonic progenitor cells for proximal tubule cells. Estimation from proportions of bgJ/bgJ‐type proximal tubules in total examined proximal tubules gave a pool size of approximately four primordial precursor cells for proximal tubules in both right and left kindeys. The fact that the proportion of bgJ/bgJ‐type components was comparable between the right and left kidneys of each chimera suggests that all proximal tubule cells in both right and left kidneys may originate from common primordial precursor cells.