Nephron induction--the epithelial mesenchymal interface revisited.

While more and more humoral factors are being implicated in nephrogenesis, there is no detailed knowledge of the morphological structures at the interface of the nephron inducer and the surrounding mesenchyme. Hence we examined this area in the cortex of neonatal rabbit kidneys by scanning and transmission electron microscopy. Our interest was focused on the basal aspect of the collecting duct ampulla and the surrounding competent mesenchyme where morphogenic signals are exchanged during nephron induction. Close contact between these two tissues is assumed during nephrogenesis to allow direct cellular contact or diffusion of soluble factors across a short distance. However, our data show the presence a wide cleft around the collecting duct ampulla spatially separating the inducer and the competent mesenchyme during nephron induction. This cleft is filled with a characteristic fibrillar mesh-work.