Deletion of Notch Signaling in the Developing Mouse Kidney Results in Expanded Expression of Arf6, Reduced Expression of E-cadherin, and Dilation of Collecting Ducts

Background: The Notch pathway is an evolutionary conserved signaling pathway that affects cellular differentiation and proliferation. Notch signaling regulates proximal/distal patterning of the nephron in the mammalian kidney. There are four Notch receptors and five ligands, and during kidney development, Notch receptors are activated by binding to ligands on neighboring cells. This results in a series of proteolytic cleavages that lead to the expression of Notch target genes. Deletion of Notch signaling in the developing collecting duct results in collecting duct dilatations and hydronephrosis. While cells lining the medullary cavity formed from hydronephrosis are highly proliferative, cells lining the cortical dilations do not label with markers of proliferation, and the cell cycle regulator Cux1 is reduced in these cells. Methods: To determine whether the dilated collecting ducts in Notch mutant kidneys, called RBPJ/kCD, resulted from changes in cell-cell interactions we evaluated the expression of the ADP-ribosylation factor GTPase Arf6 and its target of regulation, E-cadherin. To determine whether reduced Notch signaling had an effect on ciliogenesis, cilia morphology was assessed by immunofluorescence labeling of alpha-tubulin. Results: Newborn RBPJ/kCD mice exhibited medullary and cortical dilatations. Staining with DBA lectin and cytokeratin confirmed the collecting duct origin of the dilatations. Postnatal day 14 (P14), RBPJ/kCD mice exhibited hydronephrosis and cortical dilatations. Cells lining the dilated collecting ducts exhibited expanded expression of the ADP-ribosylation factor GTPase Arf6, which is normally restricted to the apical membranes. This was associated with a reduction in the expression of E-cadherin in the RBPJ/kCD collecting ducts. However, no differences in N-cadherin expression were observed. In addition, there was no difference in cilia length between wild type and RBPJ/kCD mice. Conclusion: Taken together, our results suggest that Notch signaling is required for normal kidney collecting duct development, and that reduced Notch signaling may disrupt cell-cell interactions leading to hydronephrosis.