CaMK-II is a PKD2 target that promotes pronephric kidney development and stabilizes cilia

Intracellular Ca²⁺ signals influence gastrulation, neurogenesis and organogenesis through pathways that are still being defined. One potential Ca²⁺ mediator of many of these morphogenic processes is CaMK-II, a conserved calmodulin-dependent protein kinase. Prolonged Ca²⁺ stimulation converts CaMK-II into an activated state that, in the zebrafish, is detected in the forebrain, ear and kidney. Autosomal dominant polycystic kidney disease has been linked to mutations in the Ca²⁺-conducting TRP family member PKD2, the suppression of which in vertebrate model organisms results in kidney cysts. Both PKD2-deficient and CaMK-II-deficient zebrafish embryos fail to form pronephric ducts properly, and exhibit anterior cysts and destabilized cloacal cilia. PKD2 suppression inactivates CaMK-II in pronephric cells and cilia, whereas constitutively active CaMK-II restores pronephric duct formation in pkd2 morphants. PKD2 and CaMK-II deficiencies are synergistic, supporting their existence in the same genetic pathway. We conclude that CaMK-II is a crucial effector of PKD2 Ca²⁺ that both promotes morphogenesis of the pronephric kidney and stabilizes primary cloacal cilia.