Differentiation of metanephric tubules following a short transfilter induction pulse.

Undifferentiated metanephric mesenchymes, when grown in transfilter contact with an inductor tissue, differentiate into epithelial kidney tubules. The segregation of these tubules into the different segments of the nephron was studied.In explants grown in continuous transfilter contact with the inductor, immunohistological and histochemical markers specific for the glomerular epithelial, proximal tubule, and distal tubule cells appeared by 4 1/2 to 5 days, 4 days, and 5 days of culture, respectively. Electron microscopy confirmed segmentation of the tubules: Avascular glomeruli with glomerular basement membrane material, proximal tubules with brush border formation, and distal tubules were revealed in the explants after 5 days of culture.A short (18 h) transfilter induction pulse, followed by a prolonged subculture in the absence of the inductor, resulted sulted in the formation of only a small number of tubules in about half of the explants while the rest remained undifferentiated. These scarce tubules showed the markers specific for the proximal tubules only. The segregation of all three aspects of the nephron seems to be programmed during the transfilter culture, but apparently the time needed for the induction of the different segments varies.