Inv acts as a molecular anchor for Nphp3 and Nek8 in the proximal segment of primary cilia

Abstract

A primary cilium is an antenna-like structure extending from the surface of most vertebrate cells. It is structurally divided along its vertical axis into sub-compartments that include the ciliary tip, the shaft, the ciliary necklace segment, the transitional zone and the basal body. We recently discovered that the shaft of the primary cilia has a distinct molecular compartment, termed the "Inv compartment", which is characterized by the accumulation of Inv at the base of primary cilia. Inv was discovered as a causative gene in inv mutant mice. It was later found to be responsible for the infantile type of nephronophthisis (NPHP2). Nephronophthisis (NPHP) is an autosomal recessive kidney disease. Nine causative genes have been identified, with all examined products thought to function in cilia, basal body and/or centrioles. However, their exact intra-ciliary localization and relationship have not been clear. Here, we report that products of Nphp3 and Nek8 (the mouse orthologs of the causative genes for NPHP3 and NPHP9, respectively) localize to the Inv compartment. We also show that Inv is essential for the compartmental localization of Nphp3 and Nek8, whereas localization of Inv does not require Nphp3 or Nek8. Nphp1 and Nphp4 also localize at the proximal region of the cilium, but not in Inv compartment. Our results indicate that Inv acts as an anchor for Nphp3 and Nek8 in the Inv compartment, and suggest that Inv compartment is a candidate site for intra-ciliary interaction of Inv, Nphp3 and Nek8.

Loss of the Ciliary Kinase Nek8 Causes Left-Right Asymmetry Defects

“…1,52,53 NEK8 has been identified as an interacting partner of each of the mouse protein counterparts: NEK8 and PC2 reciprocally coimmunoprecipitate from kidney and cell lysates, 37 and NEK8 has been shown to colocalize with inversin and NHPH3 in the base of the cilium in an inversin-dependent manner. 35 The association of NEK8 with each of these proteins is intriguing due to the similarities and some of the differences we identified in the jck and Nek8-null mouse models compared with Pkd2, inversin, and Nphp3 mutants.…”

“…8,33 Similarly, NEK8 localizes to the base of renal cilia and is thus far the only kinase that has been localized to the ciliary axoneme. 34,35 Cilia defects are indeed present in jck cystic renal epithelia and cells cultured from affected kidneys; mutant cilia are elongated and exhibit enhanced ciliary localization of PC1 and PC2 compared with wild-type cilia. 36,37 In addition, PC2 is hyperphosphorylated in jck kidneys and both wild-type and mutant NEK8 coimmunoprecipitate with PC2 from kidney lysates, suggesting that these proteins perform critical cooperative functions.…”

An ARL3–UNC119–RP2 GTPase cycle targets myristoylated NPHP3 to the primary cilium

“…It encodes a protein with a conserved position 2 glycine, which we predict here to be N-terminally myristoylated, and has also been shown to localize to a distinct region of the primary cilium (Shiba et al 2010). Loss-of-function mutation of Nphp3 results in embryonic lethality, and a hypomorphic mutation of Nphp3 is the causative mutation in the pcy mouse, a classic cystic kidney disease model (Olbrich et al 2003).…”

Cilia and coordination of signaling networks during heart development

“…[52][53][54][55][56][57][58][59][60][61] In this regard, NPHP2/inversin recruits and anchors NPHP3, NPHP9/Nek8, and the newly identified NPHP protein, Anks6, to a distinct region in the proximal cilium, the inversin compartment, and integrity of this module is essential for correct laterality establishment in organisms from zebrafish to humans. 15,[62][63][64][65][66][67][68] Inversin was first discovered for its role in L-R establishment 62 and, presumably, the inversin compartment impinges on the function of motile and/or sensory cilia at the embryonic node, 67,69 which is critical in breaking the embryonic bilateral symmetry through the generation of a net leftward flow of the embryonic fluid during gastrulation 8 (see also below). Consequently, NPHP patients occasionally present with laterality defects and associated complex CHD.…”