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

Abstract

A missense mutation in mouse Nek8, which encodes a ciliary kinase, produces the juvenile cystic kidneys (jck) model of polycystic kidney disease, but the functions of Nek8 are incompletely understood. Here, we generated a Nek8-null allele and found that homozygous mutant mice die at birth and exhibit randomization of left-right asymmetry, cardiac anomalies, and glomerular kidney cysts. The requirement for Nek8 in left-right patterning is conserved, as knockdown of the zebrafish ortholog caused randomized heart looping. Ciliogenesis was intact in Nek8-deficient embryos and cells, but we observed misexpression of left-sided marker genes early in development, suggesting that nodal ciliary signaling was perturbed. We also generated jck/Nek8 compound heterozygotes; these mutants developed less severe cystic disease than jck homozygotes and provided genetic evidence that the jck allele may encode a gain-of-function protein. Notably, NEK8 and polycystin-2 (PC2) proteins interact, and we found that Nek8 2/2 and Pkd2 2/2 embryonic phenotypes are strikingly similar. Nek8-deficient embryos and cells did express PC2 normally, which localized properly to the cilia. However, similar to cells lacking PC2, NEK8-depleted inner medullary collecting duct cells exhibited a defective response to fluid shear, suggesting that NEK8 may play a role in mediating PC2-dependent signaling.

Conserved Ankyrin Repeat Proteins and Their NIMA Kinase Partners Regulate Extracellular Matrix Remodeling and Intracellular Trafficking inCaenorhabditis elegans

“…In mammals, mutations affecting NEK8/NEKL-2, ANKS6/MLT-2, INVS/MLT-4, and ANKS3/MLT-3 have been directly linked to a class of diseases termed ciliopathies, which result from defects in the formation of primary cilia Otto et al 2008Otto et al , 2011Trapp et al 2008;Halbritter et al 2013;Hoff et al 2013;Delestre et al 2015). These include kidney disorders, such as nephronophthisis type 2 (Otto et al 2003) and juvenile cystic kidney disease (Liu et al 2002), as well as situs inversus, cardiovascular abnormalities, liver fibrosis, and defects in other organ systems Hoff et al 2013;Manning et al 2013). These findings, as well as the expression of NEK8, INVS, ANKS6, and ANKS3 in the proximal ciliary compartment (Shiba et al 2009(Shiba et al , 2010Hoff et al 2013;Delestre et al 2015), have led to the view that these proteins function primarily to control cilia formation.…”

“…NEKL-2 is orthologous to mammalian NEK8, which has been implicated in ciliogenesis Quarmby and Mahjoub 2005;Otto et al 2008;Shiba et al 2010;Zalli et al 2012). Correspondingly, mutations in NEK8 can lead to organogenesis defects resulting from ciliopathies Otto et al 2008Otto et al , 2011Trapp et al 2008;McCooke et al 2012;Halbritter et al 2013;Hoff et al 2013;Manning et al 2013;Delestre et al 2015). NEKL-3 is the C. elegans ortholog of mammalian paralogs NEK6 and NEK7, which have been reported to control several processes associated with cell division and are linked to human cancer.…”

Mechanobiology of Ciliogenesis

“…Therefore, in a human patient with a mutation in PC2, their cilia will not signal flow information appropriately, which will lead to disease. The jck (juvenile cystic kidneys) mouse model for PKD is defective in Nek8, a PC2-interacting kinase, and it has been shown that this kinase is also required for sensing fluid shear forces (Manning et al 2013), which further supports the link between force sensing and PKD. Although we think of this disease as resulting from a failure of cilia to detect forces acting on them, this may also be a case in which forces acting on the tissue can influence formation of cilia.…”

Cils et morphogenèse cardiaque

“…Quand la kinase ciliaire Nek8 (NIMA-related kinase 8) est mutée, les cils se forment normalement. Cependant, l'orientation de la courbure du coeur se fait au hasard chez ces mutants, qui présentent aussi des défauts de cloisonnement des chambres cardiaques et un ventricule droit à double issue [22]. Dans ces modèles animaux, l'inactivation génétique est zygotique, c'est-à-dire ubiquitaire, ce qui ne permet pas de comprendre dans quels types cellulaires les cils sont requis.…”