Figure 9

Defective convergent extension (CE) in postnatal, pre-cystic tubules of Cd79a-Tsc1 knockout (KO) kidneys. (a) Diagram illustrating the CE process. During tubular formation, the orientation of cell elongation switches from a medio-lateral to a proximal–distal direction through the formation and resolution of an intercalating rosette state. Angles (red) are measured between the cell elongation axis (green arrow) and the tubule elongation vectors (broken black arrow). (b) Orientation of cell elongation axis at P0. Section of tubules with double-positive staining for E-cadherin (green) and DAB (not shown) are viewed from the apical side. In both control and Cd79a-Tsc1 KO tubules, the majority of epithelial cells were elongated and their long axes aligned (double-headed arrows) perpendicular to the tubular axis (dot double-headed arrows). (c) Orientation of cell elongation axis at P11. Three consecutive Z-stack images from identical tubule sections were evaluated. In controls, long axis of tubular cells was aligned to tubular axis (double-headed arrows) through rosette formation (asterisks). By contrast, in Cd79a-Tsc1 KO tubules, an increasing number of cells elongated mediolaterally to tubular axis (double-headed arrows). (d) Histogram showing postnatal changes (P0 to P11) in cell elongation axis. At P0, tubular cells of both control (n = 411) and Cd79a-Tsc1 KO mouse (n = 238) kidneys showed a bimodal distribution of cell elongation axis. About 68% (control) and 73% (Cd79a-Tsc1 KO) of cell elongation axes were perpendicular to tubular axis (within angles 45° and 90°). Over time from P7 to P11, control tubular cells shifted their long axis toward being parallel to tubular axis: 57% (P7, n = 1026) and 61% (P11, n = 796) of cells’ long axes were within an angle between 0° and 45°, thus favoring tubule elongation. By contrast, long axis of Cd79a-Tsc1 KO tubule cells was distributed more randomly. The distribution was significantly different from that of controls (at P7, P < 0.02, n = 851; at P11, P < 0.001, n = 2076). Data were obtained from a minimum 6 kidneys from at least 3 litters. Statistical differences were determined by the Kolmogorov–Smirnov and Mann–Whitney U tests.