Inappropriate p53 Activation During Development Induces Features of CHARGE Syndrome

CHARGE syndrome is a multiple anomaly disorder in which patients present with a variety of phenotypes, including ocular coloboma, heart defects, choanal atresia, retarded growth and development, genitourinary hypoplasia and ear abnormalities. Despite 70-90% of CHARGE syndrome cases resulting from mutations in the gene CHD7, which encodes an ATP-dependent chromatin remodeller, the pathways underlying the diverse phenotypes remain poorly understood. Surprisingly, our studies of a knock-in mutant mouse strain that expresses a stabilized and transcriptionally dead variant of the tumour-suppressor protein p53 (p53(25,26,53,54)), along with a wild-type allele of p53 (also known as Trp53), revealed late-gestational embryonic lethality associated with a host of phenotypes that are characteristic of CHARGE syndrome, including coloboma, inner and outer ear malformations, heart outflow tract defects and craniofacial defects. We found that the p53(25,26,53,54) mutant protein stabilized and hyperactivated wild-type p53, which then inappropriately induced its target genes and triggered cell-cycle arrest or apoptosis during development. Importantly, these phenotypes were only observed with a wild-type p53 allele, as p53(25,26,53,54)(/-) embryos were fully viable. Furthermore, we found that CHD7 can bind to the p53 promoter, thereby negatively regulating p53 expression, and that CHD7 loss in mouse neural crest cells or samples from patients with CHARGE syndrome results in p53 activation. Strikingly, we found that p53 heterozygosity partially rescued the phenotypes in Chd7-null mouse embryos, demonstrating that p53 contributes to the phenotypes that result from CHD7 loss. Thus, inappropriate p53 activation during development can promote CHARGE phenotypes, supporting the idea that p53 has a critical role in developmental syndromes and providing important insight into the mechanisms underlying CHARGE syndrome

TALPID3/KIAA0586 Regulates Multiple Aspects of Neuromuscular Patterning During Gastrointestinal Development in Animal Models and Human

TALPID3/KIAA0586 is an evolutionary conserved protein, which plays an essential role in protein trafficking. Its role during gastrointestinal (GI) and enteric nervous system (ENS) development has not been studied previously. Here, we analyzed chicken, mouse and human embryonic GI tissues with TALPID3 mutations. The GI tract of TALPID3 chicken embryos was shortened and malformed. Histologically, the gut smooth muscle was mispatterned and enteric neural crest cells were scattered throughout the gut wall. Analysis of the Hedgehog pathway and gut extracellular matrix provided causative reasons for these defects. Interestingly, chicken intra-species grafting experiments and a conditional knockout mouse model showed that ENS formation did not require TALPID3, but was dependent on correct environmental cues. Surprisingly, the lack of TALPID3 in enteric neural crest cells (ENCC) affected smooth muscle and epithelial development in a non-cell-autonomous manner. Analysis of human gut fetal tissues with a KIAA0586 mutation showed strikingly similar findings compared to the animal models demonstrating conservation of TALPID3 and its necessary role in human GI tract development and patterning

Phenotypic spectrum of fetal Smith-Lemli-Opitz syndrome.

International audienceThe Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive multiple congenital malformation syndrome caused by dehydrocholesterol reductase deficiency. The diagnosis is confirmed by high 7- and secondarily 8-dehydrocholesterol levels in plasma and tissues and/or by detection of biallelic mutations in the DHCR7 gene. The phenotypic spectrum of SLOS is broad, ranging from a mild phenotype combining subtle physical anomalies with behavioral and learning problems, to a perinatally lethal multiple malformations syndrome. The fetal phenotype of SLOS has been poorly described in the literature. We report a series of 10 fetuses with molecularly proven SLOS. Even in young fetuses, the facial dysmorphism appears characteristic. Genital abnormalities are rare in 46,XX subjects. Gonadal differentiation appears histologically normal and in agreement with the chromosomal sex, contrary to what has been previously stated. We observed some previously unreported anomalies: ulnar hypoplasia, vertebral segmentation anomalies, congenital pulmonary adenomatoid malformation, fused lungs, gastroschisis, holomyelia and hypothalamic hamartoma. This latter malformation proves that SLOS phenotypically overlaps with Pallister-Hall syndrome which remains clinically a major differential diagnosis of SLOS

IFT81, encoding an IFT-B core protein, as a very rare cause of a ciliopathy phenotype

Background: Bidirectional intraflagellar transport (IFT) consists of two major protein complexes, IFT-A and IFT-B. In contrast to the IFT-B complex, all components of IFT-A have recently been linked to human ciliopathies when defective. We therefore hypothesised that mutations in additional IFT-B encoding genes can be found in patients with multisystemic ciliopathies. Methods: We screened 1628 individuals with reno-ocular ciliopathies by targeted next-generation sequencing of ciliary candidate genes, including all IFT-B encoding genes. Results: Consequently, we identified a homozygous mutation in IFT81 affecting an obligatory donor splice site in an individual with nephronophthisis and polydactyly. Further, we detected a loss-of-stop mutation with extension of the deduced protein by 10 amino acids in an individual with neuronal ceroid lipofuscinosis-1. This proband presented with retinal dystrophy and brain lesions including cerebellar atrophy, a phenotype to which the IFT81 variant might contribute. Cultured fibroblasts of this latter affected individual showed a significant decrease in ciliated cell abundance compared with controls and increased expression of the transcription factor GLI2 suggesting deranged sonic hedgehog signalling. Conclusions: This work describes identification of mutations of IFT81 in individuals with symptoms consistent with the clinical spectrum of ciliopathies. It might represent the rare case of a core IFT-B complex protein found associated with human disease. Our data further suggest that defects in the IFT-B core are an exceedingly rare finding, probably due to its indispensable role for ciliary assembly in development

A common allele in RPGRIP1L is a modifier of retinal degeneration in ciliopathies

Despite rapid advances in the identification of genes involved in disease, the predictive power of the genotype remains limited, in part owing to poorly understood effects of second-site modifiers. Here we demonstrate that a polymorphic coding variant of RPGRIP1L (retinitis pigmentosa GTPase regulator-interacting protein-1 like), a ciliary gene mutated in Meckel-Gruber (MKS) and Joubert (JBTS) syndromes, is associated with the development of retinal degeneration in individuals with ciliopathies caused by mutations in other genes. As part of our resequencing efforts of the ciliary proteome, we identified several putative loss-of-function RPGRIP1L mutations, including one common variant, A229T. Multiple genetic lines of evidence showed this allele to be associated with photoreceptor loss in ciliopathies. Moreover, we show that RPGRIP1L interacts biochemically with RPGR, loss of which causes retinal degeneration, and that the Thr229-encoded protein significantly compromises this interaction. Our data represent an example of modification of a discrete phenotype of syndromic disease and highlight the importance of a multifaceted approach for the discovery of modifier alleles of intermediate frequency and effect.This work was supported by grants R01EY007961 from the National Eye Institute (H.K. and A.S.), R01HD04260 from the National Institute of Child Health and Development (N.K.), R01DK072301, R01DK075972 (N.K.), R01DK068306, R01DK064614, R01DK069274 (F.H.), NRSA fellowship F32 DK079541 (E.E.D.) from the National Institute of Diabetes, Digestive and Kidney disorders, Intramural program of NEI (A.S.), the Macular Vision Research Foundation (N.K.), the Foundation for Fighting Blindness (H.K., S.S.B., A.S. and N.K.), the Foundation for Fighting Blindness Canada (R.K.K.), Le Fonds de la recherche en sante du Québec (FRSQ) (R.K.K.), Research to Prevent Blindness (A.S.), Harold Falls Collegiate Professorship (A.S.), the Midwest Eye Banks and Transplantation Center (H.K.), the Searle Scholars Program (M.A.B.), the Deutsche Forschungsgemeinschaft (DFG grant BE 3910/4-1; C.B.) the UK Medical Research Council (grant number G0700073; C.A.J.), NIHR Biomedical Research Centre for Ophthalmology (S.S.B.) and EU-GENORET Grant LSHG-CT-2005-512036 (S.S.B.). F.H. is an investigator of the Howard Hughes Medical Institute (HHMI) and a Doris Duke Distinguished Clinical Scientist (DDCF)

Mutations in DCC cause isolated agenesis of the corpus callosum with incomplete penetrance

Brain malformations involving the corpus callosum are common in children with developmental disabilities. We identified DCC mutations in four families and five sporadic individuals with isolated agenesis of the corpus callosum (ACC) without intellectual disability. DCC mutations result in variable dominant phenotypes with decreased penetrance, including mirror movements and ACC associated with a favorable developmental prognosis. Possible phenotypic modifiers include the type and location of mutation and the sex of the individual

TMEM107 recruits ciliopathy proteins to subdomains of the ciliary transition zone and causes Joubert syndrome

The transition zone (TZ) ciliary subcompartment is thought to control cilium composition and signalling by facilitating a protein diffusion barrier at the ciliary base. TZ defects cause ciliopathies such as Meckel–Gruber syndrome (MKS), nephronophthisis (NPHP) and Joubert syndrome1 (JBTS). However, the molecular composition and mechanisms underpinning TZ organization and barrier regulation are poorly understood. To uncover candidate TZ genes, we employed bioinformatics (coexpression and co-evolution) and identified TMEM107 as a TZ protein mutated in oral–facial–digital syndrome and JBTS patients. Mechanistic studies in Caenorhabditis elegans showed that TMEM-107 controls ciliary composition and functions redundantly with NPHP-4 to regulate cilium integrity, TZ docking and assembly of membrane to microtubule Y-link connectors. Furthermore, nematode TMEM-107 occupies an intermediate layer of the TZ-localized MKS module by organizing recruitment of the ciliopathy proteins MKS-1, TMEM-231 (JBTS20) and JBTS-14 (TMEM237). Finally, MKS module membrane proteins are immobile and super-resolution microscopy in worms and mammalian cells reveals periodic localizations within the TZ. This work expands the MKS module of ciliopathy-causing TZ proteins associated with diffusion barrier formation and provides insight into TZ subdomain architecture

Fatty acid oxidation in the human fetus: implications for fetal and adult disease

Studies in the last few years have shown a remarkably high activity of fatty acid oxidation (FAO) enzymes in human placenta. We have recently shown mRNA expression as well as enzymatic activity of long-chain FAO enzymes in the human embryo and fetus. In this study we show activity of the FAO enzymes carnitine palmitoyltranferase 1, medium-chain acyl-CoA dehydrogenase and short-chain hydroxyacyl-CoA dehydrogenase in embryonic and fetal tissues. In addition, we show the presence of different acylcarnitines in fetal liver and kidney, which substantiates the notion that the mitochondrial FAO enzymes are not only present in human fetal tissues but also metabolically active. In a glucose-rich environment FAO might be necessary for additional ATP production from fatty acids, but also for the breakdown of fatty acids that are products of the turnover of membranes in the growing fetus. The importance of FAO in the human embryo and fetus is further stressed by the fact that a higher frequency of prematurity, intrauterine growth retardation, fetal morbidity and intrauterine death is noted in long-chain FAO defects. Furthermore, in animal studies, gestational loss during early embryonic development has been observed as a consequence of disturbed FAO. Finally, there are indications that regulation of activity of FAO during fetal development might not only be important for fetal life but may also have implications for health and disease in adulthoo

Expression of PKD1 and PKD2 Transcripts and Proteins in Human Embryo and during Normal Kidney Development

Autosomal-dominant polycystic kidney disease, one of the most frequent human genetic disorders, is genetically heterogeneous. Most cases result from mutations of PKD1 or PKD2 encoding polycystin-1 or polycystin-2, respectively. Polycystin-1 is a large transmembrane protein containing several domains involved in cell-cell and/or cell-matrix interactions. Polycystin-2 is transmembrane glycoprotein sharing homology with some families of cation channels. Despite a large number of reports, the tissue distribution of these two proteins, especially of polycystin-1, is still debated. We investigated the expression pattern of PKD1 and PKD2 transcripts and proteins during human embryogenesis and kidney development, using Northern blot analysis, in situ hybridization, and immunohistochemical methods. For each gene, the expression pattern of transcripts and protein was concordant. In human 5- to 6-week-old embryos, both genes are widely expressed, mainly in neural tissue, cardiomyocytes, endodermal derivatives, and mesonephros. At this age, PKD2 but not PKD1 expression is observed in the ureteric bud and the uninduced metanephros. Thereafter, PKD2 is diffusely expressed at all stages of nephron development, whereas high PKD1 expression first appears in differentiated proximal tubules. Proximal tubule expression of both genes decreases from weeks 20 to 24 onwards. PKD1 transcripts, later restricted to distal tubules in fetal nephrogenesis, are no longer detected in adult kidneys, which nevertheless maintain a faint expression of polycystin-1, whereas persistent expression of PKD2 transcripts and protein is observed throughout nephrogenesis. Overall, contrary to previous observations, we found profound differences in the spatiotemporal expression of PKD1 and PKD2 during nephrogenesis, PKD2 being expressed earlier and more diffusely than PKD1. These data suggest that polycystins could interact with different partners, at least during kidney development