The highly conserved FOXJ1 target CFAP161 is dispensable for motile ciliary function in mouse and Xenopus.

Cilia are protrusions of the cell surface and composed of hundreds of proteins many of which are evolutionary and functionally well conserved. In cells assembling motile cilia the expression of numerous ciliary components is under the control of the transcription factor FOXJ1. Here, we analyse the evolutionary conserved FOXJ1 target CFAP161 in Xenopus and mouse. In both species Cfap161 expression correlates with the presence of motile cilia and depends on FOXJ1. Tagged CFAP161 localises to the basal bodies of multiciliated cells of the Xenopus larval epidermis, and in mice CFAP161 protein localises to the axoneme. Surprisingly, disruption of the Cfap161 gene in both species did not lead to motile cilia-related phenotypes, which contrasts with the conserved expression in cells carrying motile cilia and high sequence conservation. In mice mutation of Cfap161 stabilised the mutant mRNA making genetic compensation triggered by mRNA decay unlikely. However, genes related to microtubules and cilia, microtubule motor activity and inner dyneins were dysregulated, which might buffer the Cfap161 mutation.

The FOXJ1 target Cfap206 is required for sperm motility, mucociliary clearance of the airways and brain development.

Cilia are complex cellular protrusions consisting of hundreds of proteins. Defects in ciliary structure and function, many of which have not been characterised molecularly, cause ciliopathies: a heterogeneous group of human syndromes. Here, we report on the FOXJ1 target gene Cfap206, orthologues of which so far have only been studied in Chlamydomonas and Tetrahymena In mouse and Xenopus, Cfap206 was co-expressed with and dependent on Foxj1 CFAP206 protein localised to the basal body and to the axoneme of motile cilia. In Xenopus crispant larvae, the ciliary beat frequency of skin multiciliated cells was enhanced and bead transport across the epidermal mucociliary epithelium was reduced. Likewise, Cfap206 knockout mice revealed ciliary phenotypes. Electron tomography of immotile knockout mouse sperm flagella indicated a role in radial spoke formation reminiscent of FAP206 function in Tetrahymena Male infertility, hydrocephalus and impaired mucociliary clearance of the airways in the absence of laterality defects in Cfap206 mutant mice suggests that Cfap206 may represent a candidate for the subgroup of human primary ciliary dyskinesias caused by radial spoke defects.

CFAP157 is a murine downstream effector of FOXJ1 that is specifically required for flagellum morphogenesis and sperm motility.

Motile cilia move extracellular fluids or mediate cellular motility. Their function is essential for embryonic development, adult tissue homeostasis and reproduction throughout vertebrates. FOXJ1 is a key transcription factor for the formation of motile cilia but its downstream genetic programme is only partially understood. Here, we characterise a novel FOXJ1 target, Cfap157, that is specifically expressed in motile ciliated tissues in mouse and Xenopus in a FOXJ1-dependent manner. CFAP157 protein localises to basal bodies and interacts with tubulin and the centrosomal protein CEP350. Cfap157 knockout mice appear normal but homozygous males are infertile. Spermatozoa display impaired motility and a novel phenotype: Cfap157-deficient sperm exhibit axonemal loops, supernumerary axonemal profiles with ectopic accessory structures, excess cytoplasm and clustered mitochondria in the midpiece regions, and defective axonemes along the flagella. Our study thus demonstrates an essential sperm-specific function for CFAP157 and suggests that this novel FOXJ1 effector is part of a mechanism that acts during spermiogenesis to suppress the formation of supernumerary axonemes and ensures a correct ultrastructure.

Tumor Specific Epigenetic Silencing of Corticotropin Releasing Hormone -Binding Protein in Renal Cell Carcinoma: Association of Hypermethylation and Metastasis.

The relevance of Corticotropin Releasing Hormone (CRH)-system in human malignancies is a question of growing interest. Here we investigated hypermethylation and epigenetic silencing of the CRH-Binding Protein (CRHBP) gene in clear cell renal cell cancer (ccRCC). Relative methylation of the CRHBP CpG island (CGI) was determined in 17 tumor cell lines as well as 86 ccRCC samples and 66 paired normal tissues using pyrosequencing and quantitative methylation specific PCR of bisulfite converted DNA. Results were statistically compared with relative mRNA expression levels of CRHBP and clinicopathological parameters of patients. Re-expression of CRHBP following 5-aza-2´-deoxycytidine treatment was investigated by quantitative mRNA expression analysis. Real-time impedance analysis was applied for analysis of invasiveness of renal tumor cells following si-RNA knockdown of CRHBP expression or ectopic expression of CRHBP. We found the CRHBP CGI to be frequently methylated in tumor cell lines of renal, prostatic, and bladder cancer. Comparison of methylation in normal and paired renal cancer tissue specimens revealed hypermethylation of the CRHBP CGI in tumors (p<1*10-12). DNA methylation and decreased mRNA expression were correlated (R = 0.83, p<1*10-12). Tumor cell lines showed 5-aza-2´-deoxycytidine dependent reduction of methylation and re-expression of CRHBP was associated with altered cellular invasiveness of renal cancer cells in real-time impedance invasion assays. Hypermethylation and inverse relationship with mRNA expression were validated in silico using the TCGA network data. We describe for the first time tumor specific epigenetic silencing of CRHBP and statistical association with aggressive tumors thus suggesting the CRH system to contribute to the development of kidney cancer.

Generation of an 870 kb deletion encompassing the Skt/Etl4 locus by combination of inter- and intra-chromosomal recombination.

BACKGROUND: Etl4(lacZ) (Enhancer trap locus 4) and Skt(Gt) (Sickle tail) are lacZ reporter gene integrations into the same locus on mouse chromosome 2 targeting a gene that is expressed in the notochord of early embryos and in multiple epithelia during later development. Both insertions caused recessive mutations that resulted exclusively in mild defects in the caudal vertebral column. Since notochord-derived signals are essential for formation of the vertebral column the phenotypes suggested that the lacZ insertions interfered with some notochord-dependent aspect of vertebral development. As both insertions occurred in introns it was unclear whether they represent hypomorphic alleles or abolish gene function. Here, we have generated a definitive null allele of the Skt/Etl4 gene and analysed homozygous mutants. RESULTS: We have introduced loxP sites into three positions of the gene based on additional upstream exons that we identified, and deleted approximately 870 kb of the locus by a combination of inter- and intra-chromosomal Cre-mediated recombinations in the female germ line of mice. This deletion removes about 90 % of the coding region and results in the loss of the SKT/ETL4 protein. Similar to the Etl4(lacZ) and Skt(Gt) alleles our deletion mutants are viable and fertile and show only mild defects in caudal vertebrae due to abnormal intervertebral disc development, although with higher penetrance. No other tissue with Skt/Etl4 expression that we analysed showed obvious defects. CONCLUSION: The complete loss of Skt/Etl4 function affects only development of caudal notochord derivatives and is compensated for in its other expression domains.

O-fucosylation of DLL3 is required for its function during somitogenesis.

Delta-like 3 (DLL3) is a member of the DSL family of Notch ligands in amniotes. In contrast to DLL1 and DLL4, the other Delta-like proteins in the mouse, DLL3 does not bind in trans to Notch and does not activate the receptor, but shows cis-interaction and cis-inhibitory properties on Notch signaling in vitro. Loss of the DSL protein DLL3 in the mouse results in severe somite patterning defects, which are virtually indistinguishable from the defects in mice that lack lunatic fringe (LFNG), a glycosyltransferase involved in modifying Notch signaling. Like LFNG, DLL3 is located within the trans-Golgi, however, its biochemical function is still unclear. Here, we show that i) both proteins interact, ii) epidermal growth factor like repeats 2 and 5 of DLL3 are O-fucosylated at consensus sites for POFUT1, and iii) further modified by FNG proteins in vitro. Embryos double homozygous for null mutations in Dll3 and Lfng are phenotypically indistinguishable from the single mutants supporting a potential common function. Mutation of the O-fucosylation sites in DLL3 does not disrupt the interaction of DLL3 with LFNG or full length Notch1or DLL1, and O-fucosylation-deficient DLL3 can still inhibit Notch in cis in vitro. However, in contrast to wild type DLL3, O-fucosylation-deficient DLL3 cannot compensate for the loss of endogenous DLL3 during somitogenesis in the embryo. Together our results suggest that the cis-inhibitory activity of DLL3 observed in cultured cells might not fully reflect its assumed essential physiological property, suggest that DLL3 and LFNG act together, and strongly supports that modification of DLL3 by O-linked fucose is essential for its function during somitogenesis.

O-fucosylation of the notch ligand mDLL1 by POFUT1 is dispensable for ligand function.

Fucosylation of Epidermal Growth Factor-like (EGF) repeats by protein O-fucosyltransferase 1 (POFUT1 in vertebrates, OFUT1 in Drosophila) is pivotal for NOTCH function. In Drosophila OFUT1 also acts as chaperone for Notch independent from its enzymatic activity. NOTCH ligands are also substrates for POFUT1, but in Drosophila OFUT1 is not essential for ligand function. In vertebrates the significance of POFUT1 for ligand function and subcellular localization is unclear. Here, we analyze the importance of O-fucosylation and POFUT1 for the mouse NOTCH ligand Delta-like 1 (DLL1). We show by mass spectral glycoproteomic analyses that DLL1 is O-fucosylated at the consensus motif C²XXXX(S/T)C³ (where C² and C³ are the second and third conserved cysteines within the EGF repeats) found in EGF repeats 3, 4, 7 and 8. A putative site with only three amino acids between the second cysteine and the hydroxy amino acid within EGF repeat 2 is not modified. DLL1 proteins with mutated O-fucosylation sites reach the cell surface and accumulate intracellularly. Likewise, in presomitic mesoderm cells of POFUT1 deficient embryos DLL1 is present on the cell surface, and in mouse embryonic fibroblasts lacking POFUT1 the same relative amount of overexpressed wild type DLL1 reaches the cell surface as in wild type embryonic fibroblasts. DLL1 expressed in POFUT1 mutant cells can activate NOTCH, indicating that POFUT1 is not required for DLL1 function as a Notch ligand.

S/T phosphorylation of DLL1 is required for full ligand activity in vitro but dispensable for DLL1 function in vivo during embryonic patterning and marginal zone B cell development.

Interaction of Notch receptors with Delta- and Serrate-type ligands is an evolutionarily conserved mechanism that mediates direct communication between adjacent cells and thereby regulates multiple developmental processes. Posttranslational modifications of both receptors and ligands are pivotal for normal Notch pathway function. We have identified by mass spectrometric analysis two serine and one threonine phosphorylation sites in the intracellular domain of the mouse Notch ligand DLL1. Phosphorylation requires cell membrane association of DLL1 and occurs sequentially at the two serine residues. Phosphorylation of one serine residue most likely by protein kinase B primes phosphorylation of the other serine. A DLL1 variant, in which all three identified phosphorylated serine/threonine residues are mutated to alanine and valine, was more stable than wild-type DLL1 but had reduced relative levels on the cell surface and was more effectively cleaved in the extracellular domain. In addition, the mutant variant activated Notch1 significantly less efficient than wild-type DLL1 in a coculture assay in vitro. Mice, however, whose endogenous DLL1 was replaced with the phosphorylation-deficient triple mutant developed normally, suggesting compensatory mechanisms under physiological conditions in vivo.

Divergent functions and distinct localization of the Notch ligands DLL1 and DLL3 in vivo.

The Notch ligands Dll1 and Dll3 are coexpressed in the presomitic mesoderm of mouse embryos. Despite their coexpression, mutations in Dll1 and Dll3 cause strikingly different defects. To determine if there is any functional equivalence, we replaced Dll1 with Dll3 in mice. Dll3 does not compensate for Dll1; DLL1 activates Notch in Drosophila wing discs, but DLL3 does not. We do not observe evidence for antagonism between DLL1 and DLL3, or repression of Notch activity in mice or Drosophila. In vitro analyses show that differences in various domains of DLL1 and DLL3 individually contribute to their biochemical nonequivalence. In contrast to endogenous DLL1 located on the surface of presomitic mesoderm cells, we find endogenous DLL3 predominantly in the Golgi apparatus. Our data demonstrate distinct in vivo functions for DLL1 and DLL3. They suggest that DLL3 does not antagonize DLL1 in the presomitic mesoderm and warrant further analyses of potential physiological functions of DLL3 in the Golgi network.

Specification of vertebral identity is coupled to Notch signalling and the segmentation clock.

To further analyse requirements for Notch signalling in patterning the paraxial mesoderm, we generated transgenic mice that express in the paraxial mesoderm a dominant-negative version of Delta1. Transgenic mice with reduced Notch activity in the presomitic mesoderm as indicated by loss of Hes5 expression were viable and displayed defects in somites and vertebrae consistent with known roles of Notch signalling in somite compartmentalisation. In addition, these mice showed with variable expressivity and penetrance alterations of vertebral identities resembling homeotic transformations, and subtle changes of Hox gene expression in day 12.5 embryos. Mice that carried only one functional copy of the endogenous Delta1 gene also showed changes of vertebral identities in the lower cervical region, suggesting a previously unnoticed haploinsufficiency for Delta1. Likewise, in mice carrying a null allele of the oscillating Lfng gene, or in transgenic mice expressing Lfng constitutively in the presomitic mesoderm, vertebral identities were changed and numbers of segments in the cervical and thoracic regions were reduced, suggesting anterior shifts of axial identity. Together, these results provide genetic evidence that precisely regulated levels of Notch activity as well as cyclic Lfng activity are critical for positional specification of the anteroposterior body axis in the paraxial mesoderm.

Transcriptional oscillation of lunatic fringe is essential for somitogenesis.

A molecular oscillator that controls the expression of cyclic genes such as lunatic fringe (Lfng) in the presomitic mesoderm has been shown to be coupled with somite formation in vertebrate embryos. To address the functional significance of oscillating Lfng expression, we have generated transgenic mice expressing Lfng constitutively in the presomitic mesoderm in addition to the intrinsic cyclic Lfng activity. These transgenic lines displayed defects of somite patterning and vertebral organization that were very similar to those of Lfng null mutants. Furthermore, constitutive expression of exogenous Lfng did not compensate for the complete loss of cyclic endogenous Lfng activity. Noncyclic exogenous Lfng expression did not abolish cyclic expression of endogenous Lfng in the posterior presomitic mesoderm (psm) but affected its expression pattern in the anterior psm. Similarly, dynamic expression of Hes7 was not abolished but abnormal expression patterns were obtained. Our data are consistent with a model in which alternations of Lfng activity between ON and OFF states in the presomitic mesoderm prior to somite segmentation are critical for proper somite patterning, and suggest that Notch signaling might not be the only determinant of cyclic gene expression in the presomitic mesoderm of mouse embryos.

Cloning and characterization of the mammalian-specific nicolin 1 gene (NICN1) encoding a nuclear 24 kDa protein.

We have identified a novel mammalian gene, termed nicolin 1 gene (NICN1), that is present in human, dog and mouse, whereas it is absent from the available genome sequences of nonmammalian organisms. The NICN1 gene consists of six exons and spans about 6 kb of genomic DNA. It encodes a 213 amino acid protein that does not belong to any known protein family. Experiments using green fluorescent protein (GFP)-tagged nicolin 1 fusion proteins indicate that nicolin 1 is a nuclear protein. Northern analysis and semiquantitative RT-PCR demonstrated that the 2.5 kb NICN1 mRNA is expressed in a tissue-specific manner. The highest NICN1 expression levels are found in brain, testis, liver, and kidney. On the other hand the NICN1 expression is weak in spleen, leukocytes, small intestine and colon. The NICN1 gene is also expressed during development.