The pine-cone body: an intermediate structure between the cap mesenchyme and the renal vesicle in the developing nod mouse kidney revealed by an ultrastructural study.

Nephrogenesis is mainly characterized by the interaction of two distinct renal constituents, the ureteric bud and the metanephric mesenchyme. In this paper we describe by means of light and electron microscopic techniques the morphological events that take place during the early stages of cap mesenchymal formation. Samples of normal renal tissue were excised from newborn NOD mice and processed by standard light and electron microscopy techniques. In all samples examined we detected the presence of several cap mesenchymal aggregates in different stages of differentiation. They varied from small solid nodules with few ovoid cells to bigger pine-cone-like aggregates, characterized by a peculiar distribution and morphology of their cellular constituents. Our data highlight, for the first time, the presence of a specific cap mesenchymal structure, the pine-cone body and show, at ultrastructural level, how each cap aggregate epithelializes proceeding in stages from a condensed mesenchymal aggregate to the renal vesicle, through the intermediate "pine-cone body" stage.