Morphology of the initial nephron-collecting duct connection in mice using computerized 3D tracing and electron microscopy

• Published in: Biochemical and biophysical research communications 2019-01, Vol.509 (1), p.114-118
• Main Authors: Zhang, Ping, Gu, Ling, Cong, Jing, Zhang, Jie, Thomsen, Jesper Skovhus, Andreasen, Arne, Chang, Shi-Jie, Deng, Si-Qi, Xing, Jia, Zhai, Xiao-Yue
• Format: Article
• Language: English
• Subjects: Connecting tubule; Distal tubule; Kidney development; S-shaped body; Ureteric bud
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2018.12.079

Recently, the cellular origin of the connecting tubule (CNT) has been genetically characterized. The CNT is a segment between two embryonically different structures, the collecting duct originating from ureteric bud (UB), and the nephron derived from the cap mesenchyme. However, the cellular detail at the initial connection is limited. The present study demonstrated that the initial connection was composed of cells which were closely associated with the renal vesicle (RV), the initial nephron, and connected with the basal epithelium of the terminal UB tip at discrete points. The identification of the RV and UB tip was based on tracing of tubules on serial epoxy sections at mouse embryonic day 17.5. The cells at the initial connection were characterized by 1) irregularly-shaped nuclei and cells with cytoplasmic processes, 2) electron dense nuclei, 3) abundant intercellular spaces, 4) extensive cell-cell contacts with cell junctions, often zonulae adherences and occasionally focal fusion of opposing plasma membranes, and 5) numerous mitochondria, densely packed rosette-like polyribosomes, and widespread rER in the cytoplasm. Moreover, the tracing revealed that a terminal UB tip frequently connected to two nephrons at different developing stages. The UB tips, the initial connections, and the distal tubules of the S-shaped bodies did not express Na+-Cl− cotransporter, H+-ATPase, or aquaporin 2, while they were expressed in immature CNT of the capillary-loop stage nephrons throughout the kidney development. Consequently, the cells at the initial connection exhibit the morphological features suggestive of energy demanding, protein producing, and intercellular communicating. The cell morphology together with transporter development indicates that these cells serve several functions during the development of the initial connection, and that these functions are different from the cells' final functions as transportation. •The location of the initial connecting tubule is identified using 3D computerized tracing.•The cellular morphology of the initial connecting tubule is revealed using EM, showing the complexity of the involved cells.•A terminal UB tip frequently connected to two nephrons at different developmental stages.•Immunohistochemistry revealed expression of the water-salt and acid-base transporters in the connecting tubules.