The renal stem/progenitor cell niche is found during development at the inner side of the organ capsule. A reciprocal exchange of morphogenetic factors between epithelial and mesenchymal cells leads here to a successive anlage of nephrons. It is generally supposed that a close contact exists between involved cells and that transmission of signals occurs via diffusion. However, morphological analysis of specimens fixed in glutaraldehyde (GA) solution reveals that both types of cells are separated by an extended interface. To investigate this special cell arrangement in detail, kidneys of neonatal rabbits were fixed by GA containing lanthanum, alcian blue, cupromeronic blue, ruthenium red or tannic acid. To obtain a comparable view to the niche, parenchyma was cut along the axis of lining collecting ducts for analysis by transmission electron microscopy. Present data illustrate that fixation of specimens by GA including alcian blue, cupromeronic blue, ruthenium red or tannic acid unmasks four different textures of filigree extracellular matrix within the interface. Applied contrasting illuminates a supplementary pattern. Further on, projections of mesenchymal cells lining to epithelial cells are specifically integrated in detected matrix. Experiments are under work to elucidate, whether detected cell to cell contacts via tunneling nanotubes are involved in transmission of morphogenetic signals.
Keywords: Kidney, stem/progenitor cell niche, interstitial interface, extracellular matrix, tunneling nanotubes, exchange of morphogenetic factors, transmission electron microscopy, glutaraldehyde, alcian blue, lanthanum, cupromeronic blue, ruthenium red, tannic acid