The renal vesicle, the most primitive and first recognized nephron structure, is formed from the enlarged pretubular aggregates. Molecular patterning divides the renal vesicle into proximal and distal regions. Late-stage renal vesicles fuse with the adjacent ureteric tip via a connecting segment.
The first stage of renal vesicle formation is characterized by the progression of the mesenchymal-epithelial transition (MET) phase, and transformation of the solid pretubular mesenchymal cell aggregates into roundish epithelial structures with a central lumen. These structures are termed renal vesicles.