Cdc42 Deficiency Causes Ciliary Abnormalities and Cystic Kidneys

Abstract

Ciliogenesis and cystogenesis require the exocyst, a conserved eight-protein trafficking complex that traffics ciliary proteins. In culture, the small GTPase Cdc42 co-localizes with the exocyst at primary cilia and interacts with the exocyst component Sec10. The role of Cdc42 in vivo, however, is not well understood. Here, knockdown of cdc42 in zebrafish produced a phenotype similar to sec10 knockdown, including tail curvature, glomerular expansion, and mitogen-activated protein kinase (MAPK) activation, suggesting that cdc42 and sec10 cooperate in ciliogenesis. In addition, cdc42 knockdown led to hydrocephalus and loss of photoreceptor cilia. Furthermore, there was a synergistic genetic interaction between zebrafish cdc42 and sec10, suggesting that cdc42 and sec10 function in the same pathway. Mice lacking Cdc42 specifically in kidney tubular epithelial cells died of renal failure within weeks of birth. Histology revealed cystogenesis in distal tubules and collecting ducts, decreased ciliogenesis in cyst cells, increased tubular cell proliferation, increased apoptosis, increased fibrosis, and led to MAPK activation, all of which are features of polycystic kidney disease, especially nephronophthisis. Taken together, these results suggest that Cdc42 localizes the exocyst to primary cilia, whereupon the exocyst targets and docks vesicles carrying ciliary proteins. Abnormalities in this pathway result in deranged ciliogenesis and polycystic kidney disease.

Cdc42 regulates epithelial cell polarity and cytoskeletal function in kidney tubule development

“…It is not clear whether the cysts observed in the Ksp-cre mutants are in the collecting duct or the distal tubule. It is interesting to note that similar to Choi et al (2013), we did observe a decrease in cilia number in mutant collecting ducts. This cellular phenotype was not as penetrant as the defects in polarity and differentiation, suggesting that it might be a secondary manifestation of Cdc42 deletion.…”

“…In conclusion, we and others have shown that Cdc42 is required for normal tubulogenesis in ureteric bud and metanephric mesenchyme development of the kidney (Choi et al, 2013;Reginensi et al, 2013). Although the morphological observations are similar in all these studies, the mechanisms proposed differ.…”

“…It has previously been shown that deletion of Cdc42 in the distal tubule of the kidney using Ksp-cre induced fatal kidney failure; however, the few surviving mice developed cystogenesis associated with decreased ciliogenesis and interstitial fibrosis (Choi et al, 2013). Most of the characterization of these mice was performed within the cysts where increased cell proliferation and apoptosis associated with increased MAPK pathway activation was noted.…”

“…Cdc42 is required by Madin-Darby canine kidney (MDCK) cells to form tubules in three-dimensional (3D) culture by regulating the formation of the apical plasma membrane domain and tight junctions as well as primary ciliogenesis (Choi et al, 2013;Kim et al, 2007;Rodriguez-Fraticelli et al, 2010;Rogers et al, 2003;Zhang et al, 2001;Zuo et al, 2011). Two studies have shown that Cdc42 is essential for normal kidney development and function.…”

“…Two studies have shown that Cdc42 is essential for normal kidney development and function. In the first, Cdc42 deletion from renal tubular epithelia with the Ksp-cre (which causes cre-mediated recombination in developing nephrons and the renal collecting system) was shown to result in lethal cystic kidney disease that was attributed to abnormalities in ciliogenesis (Choi et al, 2013). In a second study, Cdc42 was deleted in the nephron progenitors using Six2-cre.…”