β‐catenin is a central component of the cadherin cell adhesion complex and plays an essential role in the Wingless/Wnt signaling pathway. In the current model of this pathway, the amount of β‐catenin (or its invertebrate homolog Armadillo) is tightly regulated and its steady‐state level outside the cadherin–catenin complex is low in the absence of Wingless/Wnt signal. Here we show that the ubiquitin‐dependent proteolysis system is involved in the regulation of β‐catenin turnover. β‐catenin, but not E‐cadherin, p120cas or α‐catenin, becomes stabilized when proteasome‐mediated proteolysis is inhibited and this leads to the accumulation of multi‐ubiquitinated forms of β‐catenin. Mutagenesis experiments demonstrate that substitution of the serine residues in the glycogen synthase kinase 3β (GSK3β) phosphorylation consensus motif of β‐catenin inhibits ubiquitination and results in stabilization of the protein. This motif in β‐catenin resembles a motif in IκB (inhibitor of NFκB) which is required for the phosphorylation‐dependent degradation of IκB via the ubiquitin–proteasome pathway. We show that ubiquitination of β‐catenin is greatly reduced in Wnt‐expressing cells, providing the first evidence that the ubiquitin–proteasome degradation pathway may act downstream of GSK3β in the regulation of β‐catenin.

In the mammalian embryo, both sexes are initially morphologically indistinguishable: specific hormones are required for sex-specific development. Mullerian inhibiting substance and testosterone secreted by the differentiating embryonic testes result in the loss of female (Mullerian) or promotion of male (Wolffian) reproductive duct development, respectively. The signalling molecule Wnt-4 is crucial for female sexual development. At birth, sexual development in males with a mutation in Wnt-4 appears to be normal; however, Wnt-4-mutant females are masculinized-the Mullerian duct is absent while the Wolffian duct continues to develop. Wnt-4 is initially required in both sexes for formation of the Mullerian duct, then Wnt-4 in the developing ovary appears to suppress the development of Leydig cells; consequently, Wnt-4-mutant females ectopically activate testosterone biosynthesis. Wnt-4 may also be required for maintenance of the female germ line. Thus, the establishment of sexual dimorphism is under the control of both local and systemic signals.

The molecular basis of nephronophthisis, the most frequent genetic cause of renal failure in children and young adults, and its association with retinal degeneration and cerebellar vermis aplasia in Joubert syndrome are poorly understood. Using positional cloning, we here identify mutations in the gene CEP290 as causing nephronophthisis. It encodes a protein with several domains also present in CENPF, a protein involved in chromosome segregation. CEP290 (also known as NPHP6) interacts with and modulates the activity of ATF4, a transcription factor implicated in cAMP-dependent renal cyst formation. NPHP6 is found at centrosomes and in the nucleus of renal epithelial cells in a cell cycle-dependent manner and in connecting cilia of photoreceptors. Abrogation of its function in zebrafish recapitulates the renal, retinal and cerebellar phenotypes of Joubert syndrome. Our findings help establish the link between centrosome function, tissue architecture and transcriptional control in the pathogenesis of cystic kidney disease, retinal degeneration, and central nervous system development.

Nephronophthisis (NPHP), an autosomal recessive cystic kidney disease, leads to chronic renal failure in children. The genes mutated in NPHP1 and NPHP4 have been identified, and a gene locus associated with infantile nephronophthisis (NPHP2) was mapped. The kidney phenotype of NPHP2 combines clinical features of NPHP and polycystic kidney disease (PKD). Here, we identify inversin (INVS) as the gene mutated in NPHP2 with and without situs inversus. We show Correspondence should be addressed to F.H. (fhilde@umich.edu). 12 These authors contributed equally to this work 13 These authors contributed equally to this work GenBank accession numbers. INVS cDNA, NM_014425; Invs cDNA, NM_010569; invs cDNA, AF465261; INVS in chromosome 9 genome contig, NT_008470.URLs. Additional information is available at http://danio.mgh.harvard.edu/blast/blast.html. Note: Supplementary information is available on the Nature Genetics website. Competing Interests Statement:The authors declare that they have no competing financial interests. NIH Public AccessAuthor Manuscript Nat Genet. Author manuscript; available in PMC 2013 August 02. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript molecular interaction of inversin with nephrocystin, the product of the gene mutated in NPHP1 and interaction of nephrocystin with β-tubulin, a main component of primary cilia. We show that nephrocystin, inversin and β-tubulin colocalize to primary cilia of renal tubular cells. Furthermore, we produce a PKD-like renal cystic phenotype and randomization of heart looping by knockdown of invs expression in zebrafish. The interaction and colocalization in cilia of inversin, nephrocystin and β-tubulin connect pathogenetic aspects of NPHP to PKD, to primary cilia function and to leftright axis determination.NPHP, an autosomal recessive cystic kidney disease, is the most frequent genetic cause for end-stage renal failure in children and young adults [1][2][3] . Causative mutations in two genes (NPHP1 and NPHP4) have been identified by positional cloning [4][5][6][7] . There is considerable interest in identifying genes associated with NPHP because its most prominent feature is development of renal interstitial fibrosis 8 , which in chronic renal disease of all origin represents the pathogenic event correlated most strongly to loss of renal function 9 . As little was known about the pathogenesis of NPHP, positional cloning was used to identify a new gene, NPHP1, mutations in which cause NPHP1 (OMIM 256100; refs. 4,5). It encodes a novel docking protein, nephrocystin [10][11][12][13] , that interacts with components of cell-cell and cell-matrix signaling, such as focal adhesion kinase 2, tensin, p130Cas and filamin, and with nephrocystin-4 or nephroretinin, the product of NPHP4, mutations in which cause NPHP4 (OMIM 606966; refs. 6,7). Identification of the genes NPHP1 and NPHP4, which are conserved in evolution including in the nematode Caenorhabditis elegans, offered new insights into mechanisms of cell-cell and cell-matrix signaling...