Evc2 is a positive modulator of Hedgehog signalling that interacts with Evc at the cilia membrane and is also found in the nucleus

Variant characterisation and clinical profile in a large cohort of patients with Ellis-van Creveld syndrome and a family with Weyers acrofacial dysostosis

BACKGROUND

Ellis-van Creveld syndrome (EvC) is a recessive disorder characterised by acromesomelic limb shortening, postaxial polydactyly, nail-teeth dysplasia and congenital cardiac defects, primarily caused by pathogenic variants in EVC or EVC2. Weyers acrofacial dysostosis (WAD) is an ultra-rare dominant condition allelic to EvC. The present work aimed to enhance current knowledge on the clinical manifestations of EvC and WAD and broaden their mutational spectrum.

METHODS

We conducted molecular studies in 46 individuals from 43 unrelated families with a preliminary clinical diagnosis of EvC and 3 affected individuals from a family with WAD and retrospectively analysed clinical data. The deleterious effect of selected variants of uncertain significance was evaluated by cellular assays.

MAIN RESULTS

We identified pathogenic variants in EVC/EVC2 in affected individuals from 41 of the 43 families with EvC. Patients from each of the two remaining families were found with a homozygous splicing variant in WDR35 and a de novo heterozygous frameshift variant in GLI3, respectively. The phenotype of these patients showed a remarkable overlap with EvC. A novel EVC2 C-terminal truncating variant was identified in the family with WAD. Deep phenotyping of the cohort recapitulated 'classical EvC findings' in the literature and highlighted findings previously undescribed or rarely described as part of EvC.

CONCLUSIONS

This study presents the largest cohort of living patients with EvC to date, contributing to better understanding of the full clinical spectrum of EvC. We also provide comprehensive information on the EVC/EVC2 mutational landscape and add GLI3 to the list of genes associated with EvC-like phenotypes.

Exploring candidate genes for heat tolerance in ovine through liver gene expression

Thermotolerance has become an essential factor in the prevention of the adverse effects of heat stress, but it varies among animals. Identifying genes related to heat adaptability traits is important for improving thermotolerance and for selecting more productive animals in hot environments. The primary objective of this research was to find candidate genes in the liver that play a crucial role in the heat stress response of Santa Ines sheep, which exhibit varying levels of heat tolerance. To achieve this goal, 80 sheep were selected based on their thermotolerance and placed in a climate chamber for 10 days, during which the average temperature was maintained at 36 °C from 10 a.m. to 4 p.m. and 28 °C from 4 p.m. to 10 a.m. A subset of 14 extreme animals, with seven thermotolerant and seven non-thermotolerant animals based on heat loss (rectal temperature), were selected for liver sampling. RNA sequencing and differential gene expression analysis were performed. Thermotolerant sheep showed higher expression of genes GPx3, RGS6, GPAT3, VLDLR, LOC101108817, and EVC. These genes were mainly related to the Hedgehog signaling pathway, glutathione metabolism, glycerolipid metabolism, and thyroid hormone synthesis. These enhanced pathways in thermotolerant animals could potentially mitigate the negative effects of heat stress, conferring greater heat resistance.

The oligodontia phenotype in a X-linked hypohidrotic ectodermal dysplasia patient with a novel EVC2 variant

Objectives

To analyse the pathogenic genes in a patient with hypohidrotic ectodermal dysplasia (HED) and explore the relationship between pathogenic genes and the oligodontia phenotype.

Methods

Clinical data and peripheral blood were collected from a patient with HED. Pathogenic genes were analysed by whole-exon sequencing (WES) and verified by Singer sequencing. The secondary and tertiary structures of the variant proteins were predicted to analyse their toxicity.

Results

The patient exhibited a severe oligodontia phenotype, wherein only two deciduous canines were left in the upper jaw. WES revealed a hemizygous EDA variant c.466C > T p.(Arg156Cys) and a novel heterozygous EVC2 variant c.1772T > C p.(Leu591Ser). Prediction of the secondary and tertiary structures of the EDA variant p.(Arg156Cys) and EVC2 variant p.(Leu591Ser) indicated impaired function of both molecules.

Conclusion

The patient demonstrated a more severe oligodontia phenotype when compared with the other patients caused by the EDA variant c.466C > T. Since Evc2 is a positive regulator of the Sonic Hedgehog (Shh) signal pathway, we speculated that the EVC2 variant p.(Leu591Ser) may play a synergistic role in the oligodontia phenotype of HED, thereby exacerbating the oligodontia phenotype. Knowledge of oligodontia caused by multiple gene variants is of great significance for understanding individual differences in oligodontia phenotypes.

Polycystin-2-dependent transcriptome reveals early response of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in polycystin genes, Pkd1 and Pkd2, but the underlying pathogenic mechanisms are poorly understood. To identify genes and pathways that operate downstream of polycystin-2 (PC2), a comprehensive gene expression database was created, cataloging changes in the transcriptome immediately following PC2 protein depletion. To explore cyst initiation processes, an immortalized mouse inner medullary collecting duct line was developed with the ability to knock out the Pkd2 gene conditionally. Genome-wide transcriptome profiling was performed using RNA sequencing in the cells immediately after PC2 was depleted and compared with isogenic control cells. Differentially expressed genes were identified, and a bioinformatic analysis pipeline was implemented. Altered expression of candidate cystogenic genes was validated in Pkd2 knockout mice. The expression of nearly 900 genes changed upon PC2 depletion. Differentially expressed genes were enriched for genes encoding components of the primary cilia, the canonical Wnt pathway, and MAPK signaling. Among the PC2-dependent ciliary genes, the transcription factor Glis3 was significantly downregulated. MAPK signaling formed a key node at the epicenter of PC2-dependent signaling networks. Activation of Wnt and MAPK signaling, concomitant with the downregulation of Glis3, was corroborated in Pkd2 knockout mice. The data identify a PC2 cilia-to-nucleus signaling axis and dysregulation of the Gli-similar subfamily of transcription factors as a potential initiator of cyst formation in ADPKD. The catalog of PC2-regulated genes should provide a valuable resource for future ADPKD research and new opportunities for drug development.NEW & NOTEWORTHY Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease. Mutations in polycystin genes cause the disease, but the underlying mechanisms of cystogenesis are unknown. To help fill this knowledge gap, we created an inducible cell model of ADPKD and assembled a catalog of genes that respond in immediate proximity to polycystin-2 depletion using transcriptomic profiling. The catalog unveils a ciliary signaling-to-nucleus axis proximal to polycystin-2 dysfunction, highlighting Glis, Wnt, and MAPK signaling.

EVC-EVC2 complex stability and ciliary targeting are regulated by modification with ubiquitin and SUMO

Ellis van Creveld syndrome and Weyers acrofacial dysostosis are two rare genetic diseases affecting skeletal development. They are both ciliopathies, as they are due to malfunction of primary cilia, microtubule-based plasma membrane protrusions that function as cellular antennae and are required for Hedgehog signaling, a key pathway during skeletal morphogenesis. These ciliopathies are caused by mutations affecting the EVC-EVC2 complex, a transmembrane protein heterodimer that regulates Hedgehog signaling from inside primary cilia. Despite the importance of this complex, the mechanisms underlying its stability, targeting and function are poorly understood. To address this, we characterized the endogenous EVC protein interactome in control and Evc-null cells. This proteomic screen confirmed EVC's main known interactors (EVC2, IQCE, EFCAB7), while revealing new ones, including USP7, a deubiquitinating enzyme involved in Hedgehog signaling. We therefore looked at EVC-EVC2 complex ubiquitination. Such ubiquitination exists but is independent of USP7 (and of USP48, also involved in Hh signaling). We did find, however, that monoubiquitination of EVC-EVC2 cytosolic tails greatly reduces their protein levels. On the other hand, modification of EVC-EVC2 cytosolic tails with the small ubiquitin-related modifier SUMO3 has a different effect, enhancing complex accumulation at the EvC zone, immediately distal to the ciliary transition zone, possibly via increased binding to the EFCAB7-IQCE complex. Lastly, we find that EvC zone targeting of EVC-EVC2 depends on two separate EFCAB7-binding motifs within EVC2's Weyers-deleted peptide. Only one of these motifs had been characterized previously, so we have mapped the second herein. Altogether, our data shed light on EVC-EVC2 complex regulatory mechanisms, with implications for ciliopathies.

Identification of Compound Heterozygous EVC2 Gene Variants in Two Mexican Families with Ellis-van Creveld Syndrome

BACKGROUND

Ellis-van Creveld syndrome (EvCS) is an autosomal recessive ciliopathy with a disproportionate short stature, polydactyly, dystrophic nails, oral defects, and cardiac anomalies. It is caused by pathogenic variants in the EVC or EVC2 genes. To obtain further insight into the genetics of EvCS, we identified the genetic defect for the EVC2 gene in two Mexican patients.

METHODS

Two Mexican families were enrolled in this study. Exome sequencing was applied in the probands to screen potential genetic variant(s), and then Sanger sequencing was used to identify the variant in the parents. Finally, a prediction of the three-dimensional structure of the mutant proteins was made.

RESULTS

One patient has a compound heterozygous EVC2 mutation: a novel heterozygous variant c.519_519 + 1delinsT inherited from her mother, and a heterozygous variant c.2161delC (p.L721fs) inherited from her father. The second patient has a previously reported compound heterozygous EVC2 mutation: nonsense mutation c.645G > A (p.W215*) in exon 5 inherited from her mother, and c.273dup (p.K92fs) in exon 2 inherited from her father. In both cases, the diagnostic was Ellis-van Creveld syndrome. Three-dimensional modeling of the EVC2 protein showed that truncated proteins are produced in both patients due to the generation of premature stop codons.

CONCLUSION

The identified novel heterozygous EVC2 variants, c.2161delC and c.519_519 + 1delinsT, were responsible for the Ellis-van Creveld syndrome in one of the Mexican patients. In the second Mexican patient, we identified a compound heterozygous variant, c.645G > A and c.273dup, responsible for EvCS. The findings in this study extend the EVC2 mutation spectrum and may provide new insights into the EVC2 causation and diagnosis with implications for genetic counseling and clinical management.

Ellis-Van Creveld Syndrome: Clinical and Molecular Analysis of 50 Individuals

BACKGROUND

Ellis-Van Creveld (EVC) syndrome is one of the entities belonging to the skeletal ciliopathies short rib-polydactyly subgroup. Major signs are ectodermal dysplasia, chondrodysplasia, polydactyly and congenital cardiopathy, with a high degree of variability in phenotypes ranging from lethal to mild clinical presentations. The EVC and EVC2 genes are the major genes causative of EVC syndrome. However, an increased number of genes involved in the ciliopathy complex have been identified in EVC syndrome, leading to a better understanding of its physiopathology, namely, WDR35, GLI1, DYNC2LI1, PRKACA, PRKACB and SMO. They all code for proteins located in the primary cilia, playing a key role in signal transduction of the Hedgehog pathways.

METHODS

The aim of this study was the analysis of 50 clinically identified EVC cases from 45 families to further define the phenotype and molecular bases of EVC.

RESULTS

Our detection rate in the cohort of 45 families was of 91.11%, with variants identified in EVC/EVC2 (77.8%), DYNC2H1 (6.7%), DYNC2LI1 (2.2%), SMO (2.2%) or PRKACB (2.2%). No distinctive feature was remarkable of a specific genotype-phenotype correlation. Interestingly, we identified a high proportion of heterozygous deletions in EVC/EVC2 of variable sizes (26.92%), mostly inherited from the mother, and probably resulting from recombinations involving Alu sequences.

CONCLUSION

We confirmed that EVC and EVC2 are the major genes involved in the EVC phenotype and highlighted the high prevalence of previously unreported CNVs (Copy Number Variation).

Dental Anomalies in Ciliopathies: Lessons from Patients with BBS2, BBS7, and EVC2 Mutations

Objective: To investigate dental anomalies and the molecular etiology of a patient with Ellis−van Creveld syndrome and two patients with Bardet−Biedl syndrome, two examples of ciliopathies. Patients and Methods: Clinical examination, radiographic evaluation, whole exome sequencing, and Sanger direct sequencing were performed. Results: Patient 1 had Ellis−van Creveld syndrome with delayed dental development or tooth agenesis, and multiple frenula, the feature found only in patients with mutations in ciliary genes. A novel homozygous mutation in EVC2 (c.703G>C; p.Ala235Pro) was identified. Patient 2 had Bardet−Biedl syndrome with a homozygous frameshift mutation (c.389_390delAC; p.Asn130ThrfsTer4) in BBS7. Patient 3 had Bardet−Biedl syndrome and carried a heterozygous mutation (c.389_390delAC; p.Asn130ThrfsTer4) in BBS7 and a homozygous mutation in BBS2 (c.209G>A; p.Ser70Asn). Her clinical findings included global developmental delay, disproportionate short stature, myopia, retinitis pigmentosa, obesity, pyometra with vaginal atresia, bilateral hydronephrosis with ureteropelvic junction obstruction, bilateral genu valgus, post-axial polydactyly feet, and small and thin fingernails and toenails, tooth agenesis, microdontia, taurodontism, and impaired dentin formation. Conclusions: EVC2, BBS2, and BBS7 mutations found in our patients were implicated in malformation syndromes with dental anomalies including tooth agenesis, microdontia, taurodontism, and impaired dentin formation.

Novel large deletion involving EVC and EVC2 in Ellis-van Creveld syndrome

Ellis-van Creveld syndrome is an autosomal recessive skeletal dysplasia that is characterized by thoracic hypoplasia, polydactyly, oral abnormalities, and congenital heart disease. It is caused by pathogenic variants in the EVC or EVC2 genes. We report a case of a newborn with a compound heterozygous variant comprising NM_147127.5: c.1991dup:[p.Lys665Glufs*10] in the EVC2 gene and a novel large deletion involving exon 1 in EVC and exons 1-7 in EVC2.

Transcriptome analysis of cervical cancer exosomes and detection of HPVE6*I transcripts in exosomal RNA

Background

Exosomes play a key role in cell-to-cell communication and are integral component of the tumor microenvironment. Recent observations suggest transfer of RNA through tumor-derived exosomes that can potentially translate into regulatory proteins in the recipient cells. Role of cervical cancer-derived exosomes and their transcript cargo is poorly understood.

Materials and methods

The total RNA of exosomes from HPV-positive (SiHa and HeLa) and HPV-negative (C33a) cervical cancer cell lines were extracted and the transcripts were estimated using Illumina HiSeq X. Further, validation of HPV transcripts were performed using RT-PCR.

Results

3099 transcripts were found to be differentially-exported in HPV-positive vs. HPV-negative exosomes (p value <0.05). Analysis of top 10 GO terms and KEGG pathways showed enrichment of transcripts belonging to axon guidance and tumor innervation in HPV-positive exosomes. Among top 20 overexpressed transcripts, EVC2, LUZP1 and ANKS1B were the most notable due to their involvement in Hh signaling, cellular migration and invasion, respectively. Further, low levels of HPV-specific reads were detected. RT-PCR validation revealed presence of E6*I splice variant of HPV18 in exosomal RNA of HeLa cells. The E6*I transcripts were consistently retained in exosomes obtained from HeLa cells undergoing 5-FU and cisplatin-induced oxidative stress.

Conclusion

Our data suggests the enrichment of poly-A RNA transcripts in the exosomal cargo of cervical cancer cells, which includes pro-tumorigenic cellular RNA and viral transcripts such as HPV E6, which may have clinical utility as potential exosomal biomarkers of cervical cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09262-4.

Cardiac Defects and Genetic Syndromes: Old Uncertainties and New Insights

Recent advances in understanding the genetic causes and anatomic subtypes of cardiac defects have revealed new links between genetic etiology, pathogenetic mechanisms and cardiac phenotypes. Although the same genetic background can result in different cardiac phenotypes, and similar phenotypes can be caused by different genetic causes, researchers’ effort to identify specific genotype–phenotype correlations remains crucial. In this review, we report on recent advances in the cardiac pathogenesis of three genetic diseases: Down syndrome, del22q11.2 deletion syndrome and Ellis–Van Creveld syndrome. In these conditions, the frequent and specific association with congenital heart defects and the recent characterization of the underlying molecular events contributing to pathogenesis provide significant examples of genotype–phenotype correlations. Defining these correlations is expected to improve diagnosis and patient stratification, and it has relevant implications for patient management and potential therapeutic options.

The timing of human adaptation from Neanderthal introgression

Admixture has the potential to facilitate adaptation by providing alleles that are immediately adaptive in a new environment or by simply increasing the long-term reservoir of genetic diversity for future adaptation. A growing number of cases of adaptive introgression are being identified in species across the tree of life, however the timing of selection, and therefore the importance of the different evolutionary roles of admixture, is typically unknown. Here, we investigate the spatio-temporal history of selection favoring Neanderthal-introgressed alleles in modern human populations. Using both ancient and present-day samples of modern humans, we integrate the known demographic history of populations, namely population divergence and migration, with tests for selection. We model how a sweep placed along different branches of an admixture graph acts to modify the variance and covariance in neutral allele frequencies among populations at linked loci. Using a method based on this model of allele frequencies, we study previously identified cases of adaptive Neanderthal introgression. From these, we identify cases in which Neanderthal-introgressed alleles were quickly beneficial and other cases in which they persisted at low frequency for some time. For some of the alleles that persisted at low frequency, we show that selection likely independently favored them later on in geographically separated populations. Our work highlights how admixture with ancient hominins has contributed to modern human adaptation and contextualizes observed levels of Neanderthal ancestry in present-day and ancient samples.

Ellis-van Creveld syndrome novel pathogenic variant in the EVC2 gene a patient from Turkey

Ellis-van Creveld syndrome 10-year-old Turkish girl and her parents were first degree cousins. A novel pathogenic variant (p.Glu1178Glyfs*82) was detected in the EVC2 gene in patient. She had no peg-shaped teeth, multiple frenula, and limb shortness.

Common atrium/atrioventricular canal defect and postaxial polydactyly: A mild clinical subtype of Ellis-van Creveld syndrome caused by hypomorphic mutations in the EVC gene

Clinical expression of Ellis-van Creveld syndrome (EvC) is variable and mild phenotypes have been described, including patients with mostly cardiac and limb involvement. Whether these cases are part of the EvC phenotypic spectrum or separate conditions is disputed. Herein, we describe a family with vertical transmission of atrioventricular canal defect (AVCD), common atrium, and postaxial polydactyly. Targeted sequencing of EVC, EVC2, WDR35, DYNC2LI1, and DYNC2H1 identified different compound heterozygosity in EVC genotypes in the two affected members, consisting of a nonsense (p.Arg622Ter) and a missense (p.Arg663Pro) variant in the father, and the same nonsense variant and a noncanonical splice-site in-frame change (c.1316-7A>G) in the daughter. Complementary DNA sequencing, immunoblot, and immunofluorescence experiments using patient-derived fibroblasts and Evc^-/- mouse embryonic fibroblasts showed that p.Arg622Ter is a loss-of-function mutation, whereas p.Arg663Pro and the splice-site change c.1316-7A>G are hypomorphic variants resulting in proteins that retain, in part, the ability to complex with EVC2. Our molecular and functional data demonstrate that at least in some cases the condition characterized as "common atrium/AVCD with postaxial polydactyly" is a mild form of EvC due to hypomorphic EVC mutations, further supporting the occurrence of genotype-phenotype correlations in this syndrome.

Molecular and Cellular Pathogenesis of Ellis-van Creveld Syndrome: Lessons from Targeted and Natural Mutations in Animal Models

Ellis-van Creveld syndrome (EVC; MIM ID #225500) is a rare congenital disease with an occurrence of 1 in 60,000. It is characterized by remarkable skeletal dysplasia, such as short limbs, ribs and polydactyly, and orofacial anomalies. With two of three patients first noted as being offspring of consanguineous marriage, this autosomal recessive disease results from mutations in one of two causative genes: EVC or EVC2/LIMBIN. The recent identification and manipulation of genetic homologs in animals has deepened our understanding beyond human case studies and provided critical insight into disease pathogenesis. This review highlights the utility of animal-based studies of EVC by summarizing: (1) molecular biology of EVC and EVC2/LIMBIN, (2) human disease signs, (3) dysplastic limb development, (4) craniofacial anomalies, (5) tooth anomalies, (6) tracheal cartilage abnormalities, and (7) EVC-like disorders in non-human species.

Elevated Hedgehog activity contributes to attenuated DNA damage responses in aged hematopoietic cells

Accumulation of DNA damage and myeloid-skewed differentiation characterize aging of the hematopoietic system, yet underlying mechanisms remain incompletely understood. Here, we show that aging hematopoietic progenitor cells particularly of the myeloid branch exhibit enhanced resistance to bulky DNA lesions—a relevant type of DNA damage induced by toxins such as cancer drugs or endogenous aldehydes. We identified aging-associated activation of the Hedgehog (Hh) pathway to be connected to this phenotype. Inhibition of Hh signaling reverts DNA damage tolerance and DNA damage-resistant proliferation in aged hematopoietic progenitors. Vice versa, elevating Hh activity in young hematopoietic progenitors is sufficient to impair DNA damage responses. Altogether, these findings provide experimental evidence for aging-associated increases in Hh activity driving DNA damage tolerance in myeloid progenitors and myeloid-skewed differentiation. Modulation of Hh activity could thus be explored as a therapeutic strategy to prevent DNA damage tolerance, myeloid skewing, and disease development in the aging hematopoietic system.

Genetic Basis for Congenital Heart Disease: Revisited: A Scientific Statement From the American Heart Association

This review provides an updated summary of the state of our knowledge of the genetic contributions to the pathogenesis of congenital heart disease. Since 2007, when the initial American Heart Association scientific statement on the genetic basis of congenital heart disease was published, new genomic techniques have become widely available that have dramatically changed our understanding of the causes of congenital heart disease and, clinically, have allowed more accurate definition of the pathogeneses of congenital heart disease in patients of all ages and even prenatally. Information is presented on new molecular testing techniques and their application to congenital heart disease, both isolated and associated with other congenital anomalies or syndromes. Recent advances in the understanding of copy number variants, syndromes, RASopathies, and heterotaxy/ciliopathies are provided. Insights into new research with congenital heart disease models, including genetically manipulated animals such as mice, chicks, and zebrafish, as well as human induced pluripotent stem cell-based approaches are provided to allow an understanding of how future research breakthroughs for congenital heart disease are likely to happen. It is anticipated that this review will provide a large range of health care-related personnel, including pediatric cardiologists, pediatricians, adult cardiologists, thoracic surgeons, obstetricians, geneticists, genetic counselors, and other related clinicians, timely information on the genetic aspects of congenital heart disease. The objective is to provide a comprehensive basis for interdisciplinary care for those with congenital heart disease.

Identification of a novel EVC variant in a Han-Chinese family with Ellis-van Creveld syndrome

Background

Ellis‐van Creveld syndrome (EVC), a very rare genetic skeletal dysplasia, is clinically characterized by a tetrad consisting of chondrodystrophy, polydactyly, ectodermal dysplasia, and cardiac anomalies. The aim of this study was to identify the genetic defect for EVC in a five‐generation consanguineous Han‐Chinese pedigree.

Methods

A five‐generation, 12‐member Han‐Chinese pedigree was enrolled in this study. Exome sequencing was applied in the proband to screen potential genetic variant(s), and then Sanger sequencing was used to identify the variant in family members and 200 unrelated ethnicity‐matched controls.

Results

A novel homozygous variant, c.2014C>T, p.(Q672*), in the EvC ciliary complex subunit 1 gene (EVC), was detected in the patient, which was cosegregated with the disease in the family and absent in the controls.

Conclusion

The identified novel homozygous EVC variant, c.2014C>T, p.(Q672*), was responsible for EVC in this Han‐Chinese pedigree. The findings in this study extend the EVC mutation spectrum and may provide new insights into EVC causation and diagnosis with implications for genetic counseling and clinical management.

Patched1-ArhGAP36-PKA-Inversin axis determines the ciliary translocation of Smoothened for Sonic Hedgehog pathway activation

The Sonic Hedgehog (Shh) pathway conducts primarily in the primary cilium and plays important roles in cell proliferation, individual development, and tumorigenesis. Shh ligand binding with its ciliary membrane-localized transmembrane receptor Patched1 results in the removal of Patched1 from and the translocation of the transmembrane oncoprotein Smoothened into the cilium, leading to Shh signaling activation. However, how these processes are coupled remains unknown. Here, we show that the Patched1-ArhGAP36-PKA-Inversin axis determines the ciliary translocation of Smoothened. We find that Patched1 interacts with and stabilizes the PKA negative regulator ArhGAP36 to the centrosome. Activating the Shh pathway results in the removal of ArhGAP36 from the mother centriole and the centrosomal PKA accumulation. This PKA then phosphorylates Inversin and promotes its interaction with and the ciliary translocation of Smoothened. Knockdown of Inversin disrupts the ciliary translocation of Smoothened and Shh pathway activation. These findings reveal a regulatory molecular mechanism for the initial step of Shh pathway activation.

Atrioventricular canal defect and genetic syndromes: The unifying role of sonic hedgehog

The atrioventricular canal defect (AVCD) is a congenital heart defect (CHD) frequently associated with extracardiac anomalies (75%). Previous observations from a personal series of patients with AVCD and "polydactyly syndromes" showed that the distinct morphology and combination of AVCD features in some of these syndromes is reminiscent of the cardiac phenotype found in heterotaxy, a malformation complex previously associated with functional cilia abnormalities and aberrant Hedgehog (Hh) signaling. Hh signaling coordinates multiple aspects of left-right lateralization and cardiovascular growth. Being active at the venous pole the secondary heart field (SHF) is essential for normal development of dorsal mesenchymal protrusion and AVCD formation and septation. Experimental data show that perturbations of different components of the Hh pathway can lead to developmental errors presenting with partially overlapping manifestations and AVCD as a common denominator. We review the potential role of Hh signaling in the pathogenesis of AVCD in different genetic disorders. AVCD can be viewed as part of a "developmental field," according to the concept that malformations can be due to defects in signal transduction cascades or pathways, as morphogenetic units which may be altered by Mendelian mutations, aneuploidies, and environmental causes.

Sending mixed signals: Cilia-dependent signaling during development and disease

Molecular signals are the guiding force of development, imparting direction upon cells to divide, migrate, differentiate, etc. The mechanisms by which a cell can receive and transduce these signals into measurable actions remains a 'black box' in developmental biology. Primary cilia are ubiquitous, microtubule-based organelles that dynamically extend from a cell to receive and process molecular and mechanical signaling cues. In the last decade, this organelle has become increasingly intriguing to the research community due to its ability to act as a cellular antenna, receive and transduce molecular stimuli, and initiate a cellular response. In this review, we discuss the structure of primary cilia, emphasizing how the ciliary components contribute to the transduction of signaling pathways. Furthermore, we address how the cilium integrates these signals and conveys them into cellular processes such as proliferation, migration and tissue patterning. Gaining a deeper understanding of the mechanisms used by primary cilia to receive and integrate molecular signals is essential, as it opens the door for the identification of therapeutic targets within the cilium that could alleviate pathological conditions brought on by aberrant molecular signaling.

Molecular mechanisms of suppressor of fused in regulating the hedgehog signalling pathway

Highly conserved throughout evolution, the hedgehog (Hh) signalling pathway has been demonstrated to be involved in embryonic development, stem cell maintenance and tissue homeostasis in animals ranging from invertebrates to vertebrates. In the human body, a variety of cancer types are associated with the aberrantly activated Hh signalling pathway. Multiple studies have revealed suppressor of fused (Sufu) as a key negative regulator of this signalling pathway. In vertebrates, Sufu primarily functions as a tumor suppressor factor by interacting with and inhibiting glioma-associated oncogene homologues (GLIs), which are the terminal transcription factors of the Hh signalling pathway and belong to the Kruppel family of zinc finger proteins; by contrast, the regulation of Sufu itself remains relatively unclear. In the present review article, we focus on the effects of Sufu on the Hh signalling pathway in tumourigenesis and the molecular mechanisms underlying the regulation of GLI by Sufu. In addition, the factors modulating the activity of Sufu at post-transcriptional levels are also discussed.

Biallelic mutations in DYNC2LI1 are a rare cause of Ellis-van Creveld syndrome

Ellis-van Creveld syndrome (EvC) is a chondral and ectodermal dysplasia caused by biallelic mutations in the EVC, EVC2 and WDR35 genes. A proportion of cases with clinical diagnosis of EvC, however, do not carry mutations in these genes. To identify the genetic cause of EvC in a cohort of mutation-negative patients, exome sequencing was undertaken in a family with 3 affected members, and mutation scanning of a panel of clinically and functionally relevant genes was performed in 24 additional subjects with features fitting/overlapping EvC. Compound heterozygosity for the c.2T>C (p.Met1?) and c.662C>T (p.Thr221Ile) variants in DYNC2LI1, which encodes a component of the intraflagellar transport-related dynein-2 complex previously found mutated in other short-rib thoracic dysplasias, was identified in the 3 affected members of the first family. Targeted resequencing detected compound heterozygosity for the same missense variant and a truncating change (p.Val141*) in 2 siblings with EvC from a second family, while a newborn with a more severe phenotype carried 2 DYNC2LI1 truncating variants. Our findings indicate that DYNC2LI1 mutations are associated with a wider clinical spectrum than previously appreciated, including EvC, with the severity of the phenotype likely depending on the extent of defective DYNC2LI1 function.

Whole exome sequencing identified sixty-five coding mutations in four neuroblastoma tumors

Neuroblastoma is a pediatric tumor characterized by histologic heterogeneity, and accounts for ~15% of childhood deaths from cancer. The five-year survival for patients with high-risk stage 4 disease has not improved in two decades. We used whole exome sequencing (WES) to identify mutations present in three independent high-risk stage 4 neuroblastoma tumors (COA/UAB-3, COA/UAB -6 and COA/UAB -8) and a stage 3 tumor (COA/UAB-14). Among the four tumors WES analysis identified forty-three mutations that had not been reported previously, one of which was present in two of the four tumors. WES analysis also corroborated twenty-two mutations that were reported previously. No single mutation occurred in all four tumors or in all stage 4 tumors. Three of the four tumors harbored genes with CADD scores ≥20, indicative of mutations associated with human pathologies. The average depth of coverage ranged from 39.68 to 90.27, with >99% sequences mapping to the genome. In summary, WES identified sixty-five coding mutations including forty-three mutations not reported previously in primary neuroblastoma tumors. The three stage 4 tumors contained mutations in genes encoding protein products that regulate immune function or cell adhesion and tumor cell metastasis.

The Role of Hedgehog Signalling in the Formation of the Ventricular Septum

An incomplete septation of the ventricles in the vertebrate heart that disturbes the strict separation between the contents of the two ventricles is termed a ventricular septal defect (VSD). Together with bicuspid aortic valves, it is the most frequent congenital heart disease in humans. Until now, life-threatening VSDs are usually treated surgically. To avoid surgery and to develop an alternative therapy (e.g., a small molecule therapy), it is necessary to understand the molecular mechanisms underlying ventricular septum (VS) development. Consequently, various studies focus on the investigation of signalling pathways, which play essential roles in the formation of the VS. In the past decade, several reports found evidence for an involvement of Hedgehog (HH) signalling in VS development. In this review article, we will summarise the current knowledge about the association between HH signalling and VS formation and discuss the use of such knowledge to design treatment strategies against the development of VSDs.

Extra-mitochondrial prosurvival BCL-2 proteins regulate gene transcription by inhibiting the SUFU tumour suppressor

Direct interactions between pro- and anti-apoptotic BCL-2 family members form the basis of cell death decision-making at the outer mitochondrial membrane (OMM). Here we report that three antiapoptotic BCL-2 proteins (MCL-1, BCL-2, and BCL-XL) found untethered from the OMM function as transcriptional regulators of a prosurvival and growth program. Antiapoptotic BCL-2 proteins engage a BCL-2 homology (BH) domain sequence found in Suppressor of Fused (SUFU), a tumor suppressor and antagonist of the GLI DNA binding proteins. BCL-2 proteins directly promote SUFU turnover, inhibit SUFU-GLI interaction, and induce the expression of the GLI target genes BCL-2, MCL-1, and BCL-XL. Antiapoptotic BCL-2 protein/SUFU feedforward signaling promotes cancer cell survival and growth and can be disabled with BH3 mimetics – small molecules that target antiapoptotic BCL-2 proteins. Our findings delineate a chemical strategy for countering drug resistance in GLI-associated tumors and reveal unanticipated functions for BCL-2 proteins as transcriptional regulators.

Copine-7 binds to the cell surface receptor, nucleolin, and regulates ciliogenesis and Dspp expression during odontoblast differentiation

Tooth development is a progressive process regulated by interactions between epithelial and mesenchymal tissues. Our previous studies showed that copine-7 (Cpne7), a dental epithelium-derived protein, is a signalling molecule that is secreted by preameloblasts and regulates the differentiation of preodontoblasts into odontoblasts. However, the mechanisms involved in the translocation of Cpne7 from preameloblasts to preodontoblasts and the functions of Cpne7 during odontogenesis are poorly understood. Here, we showed that the internalization of Cpne7 was mediated primarily by caveolae. This process was initiated by Cpne7 binding to the cell surface protein, nucleolin. Treatment with recombinant Cpne7 protein (rCpne7) in human dental pulp cells (hDPCs) caused an increase in the number of ciliated cells. The expression level of cilium components, Ift88 and Kif3a, and Dspp were increased by rCpne7. Treatment with Ift88 siRNA in hDPCs and MDPC-23 cells significantly down-regulated the expression of Dspp, an odontoblastic differentiation marker gene. Furthermore, the treatment with nucleolin siRNA in MDPC-23 cells decreased the expression of Dmp1, Dspp, and cilium components. Our findings suggested that the binding of Cpne7 with its receptor, nucleolin, has an important function involving Cpne7 internalization into preodontoblasts and regulation of Dspp expression through ciliogenesis during odontoblast differentiation.

Role of Primary Cilia in Odontogenesis

Primary cilium is a solitary organelle that emanates from the surface of most postmitotic mammalian cells and serves as a sensory organelle, transmitting the mechanical and chemical cues to the cell. Primary cilia are key coordinators of various signaling pathways during development and maintenance of tissue homeostasis. The emerging evidence implicates primary cilia function in tooth development. Primary cilia are located in the dental epithelium and mesenchyme at early stages of tooth development and later during cell differentiation and production of hard tissues. The cilia are present when interactions between both the epithelium and mesenchyme are required for normal morphogenesis. As the primary cilium coordinates several signaling pathways essential for odontogenesis, ciliary defects can interrupt the latter process. Genetic or experimental alterations of cilia function lead to various developmental defects, including supernumerary or missing teeth, enamel and dentin hypoplasia, or teeth crowding. Moreover, dental phenotypes are observed in ciliopathies, including Bardet-Biedl syndrome, Ellis-van Creveld syndrome, Weyers acrofacial dysostosis, cranioectodermal dysplasia, and oral-facial-digital syndrome, altogether demonstrating that primary cilia play a critical role in regulation of both the early odontogenesis and later differentiation of hard tissue-producing cells. Here, we summarize the current evidence for the localization of primary cilia in dental tissues and the impact of disrupted cilia signaling on tooth development in ciliopathies.

Exome sequencing revealed a splice site variant in the IQCE gene underlying post-axial polydactyly type A restricted to lower limb

Polydactyly is characterized by an extra supernumerary digit/toe with or without bony element. To date variants in four genes GLI3, ZNF141, MIPOL1 and PITX1 have been implicated in developing non-syndromic form of polydactyly. The present study involved characterization of large consanguineous family of Pakistani origin segregating post-axial polydactyly type A, restricted to lower limb, in autosomal recessive pattern. DNA of two affected members in the family was subjected to exome sequencing. Sanger sequencing was then followed to validate segregation of the variants in the family members. A homozygous splice acceptor site variant (c.395-1G>A) was identified in the IQCE gene, which completely co-segregated with post-axial polydactyly phenotype within the family. The homozygous variant was absent in different public variant databases, 7000 in-house exomes, 130 exomes from unrelated Pakistani individuals and 215 ethnically matched controls. Mini-gene splicing assay was used to test effect of the variant on function of the gene. The assay revealed loss of first nucleotide of exon 6, producing a -1 frameshift and a premature stop codon 22 bases downstream of the variant (p.Gly132Valfs*22). The study provided the first evidence of involvement of the IQCE gene in limbs development in humans.

Elevated Fibroblast Growth Factor Signaling Is Critical for the Pathogenesis of the Dwarfism in Evc2/Limbin Mutant Mice

Ellis-van Creveld (EvC) syndrome is a skeletal dysplasia, characterized by short limbs, postaxial polydactyly, and dental abnormalities. EvC syndrome is also categorized as a ciliopathy because of ciliary localization of proteins encoded by the two causative genes, EVC and EVC2 (aka LIMBIN). While recent studies demonstrated important roles for EVC/EVC2 in Hedgehog signaling, there is still little known about the pathophysiological mechanisms underlying the skeletal dysplasia features of EvC patients, and in particular why limb development is affected, but not other aspects of organogenesis that also require Hedgehog signaling. In this report, we comprehensively analyze limb skeletogenesis in Evc2 mutant mice and in cell and tissue cultures derived from these mice. Both in vivo and in vitro data demonstrate elevated Fibroblast Growth Factor (FGF) signaling in Evc2 mutant growth plates, in addition to compromised but not abrogated Hedgehog-PTHrP feedback loop. Elevation of FGF signaling, mainly due to increased Fgf18 expression upon inactivation of Evc2 in the perichondrium, critically contributes to the pathogenesis of limb dwarfism. The limb dwarfism phenotype is partially rescued by inactivation of one allele of Fgf18 in the Evc2 mutant mice. Taken together, our data uncover a novel pathogenic mechanism to understand limb dwarfism in patients with Ellis-van Creveld syndrome.

Expression of Evc2 in craniofacial tissues and craniofacial bone defects in Evc2 knockout mouse

OBJECTIVE

Our objectives were to determine the expression of EVC2 in craniofacial tissues and investigate the effect of Evc2 deficiency on craniofacial bones using Evc2 knockout (KO) mouse model.

DESIGN

Evc2 KO mice were generated by introducing a premature stop codon followed by the Internal Ribosomal Entry Site fused to β-galactosidase (LacZ). Samples from wild-type (WT), heterozygous (Het) and homozygous Evc2 KO mice were prepared. LacZ staining and immunohistochemistry (IHC) with anti-β-galactosidase, anti-EVC2 and anti-SOX9 antibodies were performed. The craniofacial bones were stained with alcian blue and alizarin red.

RESULTS

The LacZ activity in KO was mainly observed in the anterior parts of viscerocranium. The Evc2-expressing cells were identified in many cartilageous regions by IHC with anti-β-galactosidase antibody in KO and Het embryos. The endogenous EVC2 protein was observed in these areas in WT embryos. Double labeling with anti-SOX9 antibody showed that these cells were mainly chondrocytes. At adult stages, the expression of EVC2 was found in chondrocytes of nasal bones and spheno-occipital synchondrosis, and osteocytes and endothelial-like cells of the premaxilla and mandible. The skeletal double staining demonstrated that craniofacial bones, where the expression of EVC2 was observed, in KO had the morphological defects as compared to WT.

CONCLUSION

To our knowledge, our study was the first to identify the types of Evc2-expressing cells in craniofacial tissues. Consistent with the expression pattern, abnormal craniofacial bone morphology was found in the Evc2 KO mice, suggesting that EVC2 may be important during craniofacial growth and development.

Hedgehog receptor function during craniofacial development

The Hedgehog signalling pathway plays a fundamental role in orchestrating normal craniofacial development in vertebrates. In particular, Sonic hedgehog (Shh) is produced in three key domains during the early formation of the head; neuroectoderm of the ventral forebrain, facial ectoderm and the pharyngeal endoderm; with signal transduction evident in both ectodermal and mesenchymal tissue compartments. Shh signalling from the prechordal plate and ventral midline of the diencephalon is required for appropriate division of the eyefield and forebrain, with mutation in a number of pathway components associated with Holoprosencephaly, a clinically heterogeneous developmental defect characterized by a failure of the early forebrain vesicle to divide into distinct halves. In addition, signalling from the pharyngeal endoderm and facial ectoderm plays an essential role during development of the face, influencing cranial neural crest cells that migrate into the early facial processes. In recent years, the complexity of Shh signalling has been highlighted by the identification of multiple novel proteins that are involved in regulating both the release and reception of this protein. Here, we review the contributions of Shh signalling during early craniofacial development, focusing on Hedgehog receptor function and describing the consequences of disruption for inherited anomalies of this region in both mouse models and human populations.

Novel mutations in EVC cause aberrant splicing in Ellis-van Creveld syndrome

Ellis-van Creveld syndrome (EvC) is a rare autosomal recessive disorder characterized by disproportionate chondrodysplasia, postaxial polydactyly, nail dystrophy, dental abnormalities and in a proportion of patients, congenital cardiac malformations. Weyers acrofacial dysostosis (Weyers) is another dominantly inherited disorder allelic to EvC syndrome but with milder phenotypes. Both disorders can result from loss-of-function mutations in either EVC or EVC2 gene, and phenotypes associated with the two gene mutations are clinically indistinguishable. We present here a clinical and molecular analysis of a Chinese family manifested specific features of EvC syndrome. Sequencing of both EVC and EVC2 identified two novel heterozygous splice site mutations c.384+5G>C in intron 3 and c.1465-1G>A in intron 10 in EVC, which were inherited from mother and father, respectively. In vitro minigene expression assay, RT-PCR and sequencing analysis demonstrated that c.384+5G>C mutation abolished normal splice site and created a new cryptic acceptor site within exon 4, whereas c.1465-1G>A mutation affected consensus splice junction site and resulted in full exon 11 skipping. These two aberrant pre-mRNA splicing processes both produced in-frame abnormal transcripts that possibly led to abolishment of important functional domains. To our knowledge, this is the first report of EVC mutations that cause EvC syndrome in Chinese population. Our data revealed that EVC splice site mutations altered splicing pattern and helped elucidate the pathogenesis of EvC syndrome.

Sonic hedgehog functions upstream of disrupted-in-schizophrenia 1 (disc1): implications for mental illness

DISRUPTED-IN-SCHIZOPHRENIA (DISC1) has been one of the most intensively studied genetic risk factors for mental illness since it was discovered through positional mapping of a translocation breakpoint in a large Scottish family where a balanced chromosomal translocation was found to segregate with schizophrenia and affective disorders. While the evidence for it being central to disease pathogenesis in the original Scottish family is compelling, recent genome-wide association studies have not found evidence for common variants at the DISC1 locus being associated with schizophrenia in the wider population. It may therefore be the case that DISC1 provides an indication of biological pathways that are central to mental health issues and functional studies have shown that it functions in multiple signalling pathways. However, there is little information regarding factors that function upstream of DISC1 to regulate its expression and function. We herein demonstrate that Sonic hedgehog (Shh) signalling promotes expression of disc1 in the zebrafish brain. Expression of disc1 is lost in smoothened mutants that have a complete loss of Shh signal transduction, and elevated in patched mutants which have constitutive activation of Shh signalling. We previously demonstrated that disc1 knockdown has a dramatic effect on the specification of oligodendrocyte precursor cells (OPC) in the hindbrain and Shh signalling is known to be essential for the specification of these cells. We show that disc1 is prominently expressed in olig2-positive midline progenitor cells that are absent in smo mutants, while cyclopamine treatment blocks disc1 expression in these cells and mimics the effect of disc1 knock down on OPC specification. Various features of a number of psychiatric conditions could potentially arise through aberrant Hedgehog signalling. We therefore suggest that altered Shh signalling may be an important neurodevelopmental factor in the pathobiology of mental illness.

Generation of Evc2/Limbin global and conditional KO mice and its roles during mineralized tissue formation

Ellis-van Creveld (EvC) syndrome (OMIM 225500) is an autosomal recessive disease characterized with chondrodysplastic dwarfism in association with abnormalities in oral cavity. Ciliary proteins EVC and EVC2 have been identified as causative genes and they play an important role on Hedgehog signal transduction. We have also identified a causative gene LIMBIN for bovine chondrodysplastic dwarfism (bcd) that is later identified as the bovine ortholog of EVC2. Here, we report generation of conventional and conditional mutant Evc2/Limbin alleles that mimics mutations found in EvC patients and bcd cattle. Resulted homozygous mice showed no ciliary localization of EVC2 and EVC and displayed reduced Hedgehog signaling activity in association with skeletal and oral defects similar to the EvC patients. Cartilage-specific disruption of Evc2/Limbin resulted in similar but milder skeletal defects, whereas osteoblast-specific disruption did not cause overt changes in skeletal system. Neural crest-specific disruption of Evc2/Limbin resulted in defective incisor growth similar to that seen in conventional knockouts; however, differentiation of amelobolasts was relatively normal in the conditional knockouts. These results showcased functions of EVC2/LIMBIN during formation of mineralized tissues. Availability of the conditional allele for this gene should facilitate further detailed analyses of the role of EVC2/LIMBIN in pathogenesis of EvC syndrome. genesis 53:612-626, 2015. © 2015 Wiley Periodicals, Inc.

Specific variants in WDR35 cause a distinctive form of Ellis-van Creveld syndrome by disrupting the recruitment of the EvC complex and SMO into the cilium

Most patients with Ellis-van Creveld syndrome (EvC) are identified with pathogenic changes in EVC or EVC2, however further genetic heterogeneity has been suggested. In this report we describe pathogenic splicing variants in WDR35, encoding retrograde intraflagellar transport protein 121 (IFT121), in three families with a clinical diagnosis of EvC but having a distinctive phenotype. To understand why WDR35 variants result in EvC, we analysed EVC, EVC2 and Smoothened (SMO) in IFT-A deficient cells. We found that the three proteins failed to localize to Wdr35(-/-) cilia, but not to the cilium of the IFT retrograde motor mutant Dync2h1(-/-), indicating that IFT121 is specifically required for their entry into the ciliary compartment. Furthermore expression of Wdr35 disease cDNAs in Wdr35(-/-) fibroblasts revealed that the newly identified variants lead to Hedgehog signalling defects resembling those of Evc(-/-) and Evc2(-/-) mutants. Together our data indicate that splicing variants in WDR35, and possibly in other IFT-A components, underlie a number of EvC cases by disrupting targeting of both the EvC complex and SMO to cilia.

Epigenetic deregulation of Ellis Van Creveld confers robust Hedgehog signaling in adult T-cell leukemia

One of the hallmarks of cancer, global gene expression alteration, is closely associated with the development and malignant characteristics associated with adult T-cell leukemia (ATL) as well as other cancers. Here, we show that aberrant overexpression of the Ellis Van Creveld (EVC) family is responsible for cellular Hedgehog (HH) activation, which provides the pro-survival ability of ATL cells. Using microarray, quantitative RT-PCR and immunohistochemistry we have demonstrated that EVC is significantly upregulated in ATL and human T-cell leukemia virus type I (HTLV-1)-infected cells. Epigenetic marks, including histone H3 acetylation and Lys4 trimethylation, are specifically accumulated at the EVC locus in ATL samples. The HTLV-1 Tax participates in the coordination of EVC expression in an epigenetic fashion. The treatment of shRNA targeting EVC, as well as the transcription factors for HH signaling, diminishes the HH activation and leads to apoptotic death in ATL cell lines. We also showed that a HH signaling inhibitor, GANT61, induces strong apoptosis in the established ATL cell lines and patient-derived primary ATL cells. Therefore, our data indicate that HH activation is involved in the regulation of leukemic cell survival. The epigenetically deregulated EVC appears to play an important role for HH activation. The possible use of EVC as a specific cell marker and a novel drug target for HTLV-1-infected T-cells is implicated by these findings. The HH inhibitors are suggested as drug candidates for ATL therapy. Our findings also suggest chromatin rearrangement associated with active histone markers in ATL.

Genome-wide linkage study suggests a susceptibility locus for isolated bilateral microtia on 4p15.32-4p16.2

Microtia is a congenital deformity where the external ear is underdeveloped. Genetic investigations have identified many susceptibility genes of microtia-related syndromes. However, no causal genes were reported for isolated microtia, the main form of microtia. We conducted a genome-wide linkage analysis on a 5-generation Chinese pedigree with isolated bilateral microtia. We identified a suggestive linkage locus on 4p15.32-4p16.2 with parametric LOD score of 2.70 and nonparametric linkage score (Zmean) of 12.28 (simulated occurrence per genome scan equal to 0.46 and 0.47, respectively). Haplotype reconstruction analysis of the 4p15.32-4p16.2 region further confined the linkage signal to a 10-Mb segment located between rs12505562 and rs12649803 (9.65-30.24 cM; 5.54-15.58 Mb). Various human organ developmental genes reside in this 10-Mb susceptibility region, such as EVC, EVC2, SLC2A9, NKX3-2, and HMX1. The coding regions of three genes, EVC known for cartilage development and NKX3-2, HMX1 involved in microtia, were selected for sequencing with 5 individuals from the pedigree. Of the 38 identified sequence variants, none segregates along with the disease phenotype. Other genes or DNA sequences of the 10-Mb region warrant for further investigation. In conclusion, we report a susceptibility locus of isolated microtia, and this finding will encourage future studies on the genetic basis of ear deformity.

Deletion in the EVC2 gene causes chondrodysplastic dwarfism in Tyrolean Grey cattle

During the summer of 2013 seven Italian Tyrolean Grey calves were born with abnormally short limbs. Detailed clinical and pathological examination revealed similarities to chondrodysplastic dwarfism. Pedigree analysis showed a common founder, assuming autosomal monogenic recessive transmission of the defective allele. A positional cloning approach combining genome wide association and homozygosity mapping identified a single 1.6 Mb genomic region on BTA 6 that was associated with the disease. Whole genome re-sequencing of an affected calf revealed a single candidate causal mutation in the Ellis van Creveld syndrome 2 (EVC2) gene. This gene is known to be associated with chondrodysplastic dwarfism in Japanese Brown cattle, and dwarfism, abnormal nails and teeth, and dysostosis in humans with Ellis-van Creveld syndrome. Sanger sequencing confirmed the presence of a 2 bp deletion in exon 19 (c.2993_2994ACdel) that led to a premature stop codon in the coding sequence of bovine EVC2, and was concordant with the recessive pattern of inheritance in affected and carrier animals. This loss of function mutation confirms the important role of EVC2 in bone development. Genetic testing can now be used to eliminate this form of chondrodysplastic dwarfism from Tyrolean Grey cattle.

Primary cilia integrate hedgehog and Wnt signaling during tooth development

Many ciliopathies have clinical features that include tooth malformations but how these defects come about is not clear. Here we show that genetic deletion of the motor protein Kif3a in dental mesenchyme results in an arrest in odontogenesis. Incisors are completely missing, and molars are enlarged in Wnt1(Cre+)Kif3a(fl/fl) embryos. Although amelogenesis and dentinogenesis initiate in the molar tooth bud, both processes terminate prematurely. We demonstrate that loss of Kif3a in dental mesenchyme results in loss of Hedgehog signaling and gain of Wnt signaling in this same tissue. The defective dental mesenchyme then aberrantly signals to the dental epithelia, which prompts an up-regulation in the Hedgehog and Wnt responses in the epithelia and leads to multiple attempts at invagination and an expanded enamel organ. Thus, the primary cilium integrates Hedgehog and Wnt signaling between dental epithelia and mesenchyme, and this cilia-dependent integration is required for proper tooth development.

EFCAB7 and IQCE regulate hedgehog signaling by tethering the EVC-EVC2 complex to the base of primary cilia

The Hedgehog (Hh) pathway depends on primary cilia in vertebrates, but the signaling machinery within cilia remains incompletely defined. We report the identification of a complex between two ciliary proteins, EFCAB7 and IQCE, which positively regulates the Hh pathway. The EFCAB7-IQCE module anchors the EVC-EVC2 complex in a signaling microdomain at the base of cilia. EVC and EVC2 genes are mutated in Ellis van Creveld and Weyers syndromes, characterized by impaired Hh signaling in skeletal, cardiac, and orofacial tissues. EFCAB7 binds to a C-terminal disordered region in EVC2 that is deleted in Weyers patients. EFCAB7 depletion mimics the Weyers cellular phenotype-the mislocalization of EVC-EVC2 within cilia and impaired activation of the transcription factor GLI2. Evolutionary analysis suggests that emergence of these complexes might have been important for adaptation of an ancient organelle, the cilium, for an animal-specific signaling network.

VIDEO ABSTRACT

Cilia and coordination of signaling networks during heart development

Primary cilia are unique sensory organelles that coordinate a wide variety of different signaling pathways to control cellular processes during development and in tissue homeostasis. Defects in function or assembly of these antenna-like structures are therefore associated with a broad range of developmental disorders and diseases called ciliopathies. Recent studies have indicated a major role of different populations of cilia, including nodal and cardiac primary cilia, in coordinating heart development, and defects in these cilia are associated with congenital heart disease. Here, we present an overview of the role of nodal and cardiac primary cilia in heart development.

Hedgehog signaling from the primary cilium to the nucleus: an emerging picture of ciliary localization, trafficking and transduction

The unexpected connection between cilia and signaling is one of the most exciting developments in cell biology in the past decade. In particular, the Hedgehog (Hh) signaling pathway relies on the primary cilium to regulate tissue patterning and homeostasis in vertebrates. A central question is how ciliary localization and trafficking of Hh pathway components lead to pathway activation and regulation. In this review, we discuss recent studies that reveal the roles of ciliary regulators, components and structures in controlling the movement and signaling of Hh players. These findings significantly increase our mechanistic understanding of how the primary cilium facilitates Hh signal transduction and form the basis for further investigations to define the function of cilia in other signaling processes.

Hedgehog signaling and the cilium: in the zone

Hedgehog signaling is transduced at the primary cilium, but the precise mechanisms underlying this action are not clear. In this issue of Developmental Cell, Dorn and colleagues (2012) describe a novel mechanism for control of Hedgehog signaling by Evc proteins within the primary cilium.