Mutations in the Planar Cell Polarity gene, Fuzzy, are associated with neural tube defects in humans

The planar cell polarity (PCP) pathway is evolutionally conserved from flies to vertebrate; it controls multiple cellular processes during embryonic development. One of such processes is neurulation, which gives rise to the brain and spinal cord. Mutations in the PCP genes in mice cause a very severe neural tube defect (NTD), called craniorachischisis, establishing that the PCP pathway is an important regulator of neural tube closure.;NTDs are the second most common congenital malformation in humans. Since the etiology of NTDs in humans is complex and involves both genetic and environmental factors, the identifying of the causative genes/factors has been very difficult. Recently, however, mutations in the PCP genes, Vangl1 and Vangl2, were reported to contribute to the pathogenesis of a subset (∼2%) of human NTDs, suggesting that other genes in the same pathway may account for some cases of NTDs in humans.;Knockdown studies of another PCP gene, Fuzzy, in model animals revealed a wide spectrum of phenotypes including NTDs, defective convergent extension, abnormal Sonic hedgehog (Shh) signalling, and defects in ciliogenesis. In this project, we studied the role of Fuzzy in neural tube development in mammals as well as Fuzzy-dependent molecular mechanisms that contribute to the generation of primary cilium. We screened a human NTD cohort from Italy for mutations in Fuzzy and identified five non-synonymous disease-associated amino-acid variants. We have designed novel methods to ascertain an impact of mutations on ciliogenesis. We report here that Fuzzy mutations affect formation of primary cilium and ciliary length and impact directional cell movements. We therefore propose that mutations in Fuzzy may account for the subset of NTDs in humans.;We established that Fuzzy delivers Rab8, an essential regulator of ciliogenesis, to the cilium and propose that loss of cilia seen in Fuzzy mutant is, at least partly, due to the loss of Rab8 at the cilium. In addition, we uncovered novel molecular mechanisms whereby Fuzzy affects canonical Wnt signalling. We report here that Fuzzy interacts with DVL2, a PCP protein. Fuzzy both recruits and delivers DVL2 to the primary cilium, consequently limiting the canonical PCP pathway.