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 inter face of the nephron inducer and the surrounding mesenchyme. Hence we examin ed this area in the cortex of neonatal rabbit kidneys by scanning and trans mission electron microscopy. Our interest was focused on the basal aspect o f the collecting duct ampulla and the surrounding competent mesenchyme wher e 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. H owever, our data show the presence a wide cleft around the collecting duct ampulla spatially separating the inducer and the competent mesenchyme durin g nephron induction. This cleft is filled with a characteristic fibrillar m eshwork.