A potential molecular pathogenesis of cardiac/laterality defects in Oculo-Facio-Cardio-Dental syndrome

X-linked BCOR variants identified in Chinese Han patients with congenital heart disease

BACKGROUND

Congenital heart disease (CHD) frequently manifests as a complex phenotype and approximately one-third of cases may be caused by genetic factors. BCOR, an X-linked gene encoding the corepressor of BCL6, has been demonstrated to be closely involved in human heart development. However, whether BCOR variants represent the genetic etiology underlying CHD needs further investigation.

METHODS

We performed whole exome sequencing on CHD nuclear families and identified a candidate gene, BCOR, by robust bioinformatic analysis and medical literature searches. Targeted DNA sequencing of the candidate gene was conducted and then the association between variants and the risk of developing CHD was analyzed. The effects of BCOR mutations on gene expression, localization, protein interaction, and signaling pathways were evaluated in vitro.

RESULTS

We identified a BCOR hemizygous missense variant (c.1448C>T, p.Pro483Leu) in a male proband presented with CHD/heterotaxy. Sanger sequencing confirmed that this variant was inherited from his asymptomatic mother. Interestingly, through literature searches, we observed another novel BCOR hemizygous missense variant (c.1619G>A, p.Arg540Gln) in a CHD patient with heterotaxy, supporting the pathogenic evidence of BCOR variants. Functional experiments conducted in vitro revealed that the variant p.Pro483Leu altered the subcellular localization of BCOR protein, disrupted its interaction with BCL6, and significantly promoted cell proliferation, whereas the variant p.Arg540Gln displayed no obvious effects. Nevertheless, transcriptional analysis revealed that down-regulation of BCOR substantially enhanced the activities of mitogen-activated protein and phosphoinositide 3-kinase-AKT signaling pathways, which are closely attributed to heart development. Targeted sequencing of 932 sporadic CHD patients enriched nine variants of BCOR predicted as likely rare and damaging and a septal defect was present in 81.8% (9/11) of them, including the two probands, which was consistent with the possible phenotype caused by BCOR defects.

CONCLUSIONS

The findings of the present study indicate that variants in BCOR may predispose individuals to CHD in the Chinese Han population.

Cardiac developmental toxicity and transcriptome analyses of zebrafish (Danio rerio) embryos exposed to Mancozeb

Mancozeb (MZ), an antibacterial pesticide, has been linked to reproductive toxicity, neurotoxicity, and endocrine disruption. However, whether MZ has cardiactoxicity is unclear. In this study, the cardiotoxic effects of exposure to environment-related MZ concentrations ranging from 1.88 μM to 7.52 μM were evaluated at the larval stage of zebrafish. Transcriptome sequencing predicted the mechanism of MZ-induced cardiac developmental toxicity in zebrafish by enrichment analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). Consistent with morphological changes, the osm, pfkfb3, foxh1, stc1, and nrarpb genes may effect normal development of zebrafish heart by activating NOTCH signaling pathways, resulting in pericardial edema, myocardial fibrosis, and congestion in the heart area. Moreover, differential gene expression analysis indicated that cyp-related genes (cyp1c2 and cyp3c3) were significantly upregulated after MZ treatment, which may be related to apoptosis of myocardial cells. These results were verified by real-time quantitative RT-qPCR and acridine orange staining. Our findings suggest that MZ-mediated cardiotoxic development of zebrafish larvae may be related to the activation of Notch and apoptosis-related signaling pathways.

OFCD syndrome and extraembryonic defects are revealed by conditional mutation of the Polycomb-group repressive complex 1.1 (PRC1.1) gene BCOR

BCOR is a critical regulator of human development. Heterozygous mutations of BCOR in females cause the X-linked developmental disorder Oculofaciocardiodental syndrome (OFCD), and hemizygous mutations of BCOR in males cause gestational lethality. BCOR associates with Polycomb group proteins to form one subfamily of the diverse Polycomb repressive complex 1 (PRC1) complexes, designated PRC1.1. Currently there is limited understanding of differing developmental roles of the various PRC1 complexes. We therefore generated a conditional exon 9-10 knockout Bcor allele and a transgenic conditional Bcor expression allele and used these to define multiple roles of Bcor, and by implication PRC1.1, in mouse development. Females heterozygous for Bcor exhibiting mosaic expression due to the X-linkage of the gene showed reduced postnatal viability and had OFCD-like defects. By contrast, Bcor hemizygosity in the entire male embryo resulted in embryonic lethality by E9.5. We further dissected the roles of Bcor, focusing on some of the tissues affected in OFCD through use of cell type specific Cre alleles. Mutation of Bcor in neural crest cells caused cleft palate, shortening of the mandible and tympanic bone, ectopic salivary glands and abnormal tongue musculature. We found that defects in the mandibular region, rather than in the palate itself, led to palatal clefting. Mutation of Bcor in hindlimb progenitor cells of the lateral mesoderm resulted in 2/3 syndactyly. Mutation of Bcor in Isl1-expressing lineages that contribute to the heart caused defects including persistent truncus arteriosus, ventricular septal defect and fetal lethality. Mutation of Bcor in extraembryonic lineages resulted in placental defects and midgestation lethality. Ubiquitous over expression of transgenic Bcor isoform A during development resulted in embryonic defects and midgestation lethality. The defects we have found in Bcor mutants provide insights into the etiology of the OFCD syndrome and how BCOR-containing PRC1 complexes function in development.

A novel deletion mutation, c.1296delT in the BCOR gene, is associated with oculo-facio-cardio-dental syndrome

The purpose of the present study was to analyze the clinical phenotypes of a girl with oculo-facio-cardio-dental (OFCD) syndrome and to identify the potential pathogenic mutation responsible for her disease. The patient underwent detailed clinical examinations and phenotype data were collected over a follow-up period of 9 years. Mutation analysis of the candidate gene BCOR was performed with polymerase chain reaction and Sanger sequencing. BCOR of 60 unrelated normal individuals were also sequenced as a control group. Clinical phenotyping and follow-up study results indicate that this patient had multiple system anomalies including ocular, facial, cardiac, dental, and limb malformations. In addition, papilloma of the choroid plexus was identified, which represents the first report of this phenotype in an OFCD patient. A novel deletion mutation, c.1296delT in exon 4 of the BCOR gene, was identified in this patient and was not found in her parents or in 60 normal unrelated individuals. This deletion was a frameshift mutation and is proposed to encode a premature stop codon, thus producing a truncated protein. Our patient fitted the diagnostic criteria for OFCD syndrome and we report the first papilloma of the choroid plexus in an OFCD patient, expanding the recognized phenotypic spectrum of this disease. Meanwhile, we identified a novel deletion mutation that may cause OFCD syndrome.

A new approach to chromosome-wide analysis of X-linked markers identifies new associations in Asian and European case-parent triads of orofacial clefts

Background

GWAS discoveries on the X-chromosome are underrepresented in the literature primarily because the analytical tools that have been applied were originally designed for autosomal markers. Our objective here is to employ a new robust and flexible tool for chromosome-wide analysis of X-linked markers in complex traits. Orofacial clefts are good candidates for such analysis because of the consistently observed excess of females with cleft palate only (CPO) and excess of males with cleft lip with or without cleft palate (CL/P).

Methods

Genotypes for 14,486 X-chromosome SNPs in 1,291 Asian and 1,118 European isolated cleft triads were available from a previously published GWAS. The R-package HAPLIN enables genome-wide–level analyses as well as statistical power simulations for a range of biologic scenarios. We analyzed isolated CL/P and isolated CPO for each ethnicity in HAPLIN, using a sliding-window approach to haplotype analysis and two different statistical models, with and without X-inactivation in females.

Results

There was a larger number of associations in the Asian versus the European sample, and similar to previous reports that have analyzed the same GWAS dataset using different methods, we identified associations with EFNB1/PJA1 and DMD. In addition, new associations were detected with several other genes, among which KLHL4, TBX22, CPXCR1 and BCOR were noteworthy because of their roles in clefting syndromes. A few of the associations were only detected by one particular X-inactivation model, whereas a few others were only detected in one sex.

Discussion/Conclusion

We found new support for the involvement of X-linked variants in isolated clefts. The associations were specific for ethnicity, sex and model parameterization, highlighting the need for flexible tools that are capable of detecting and estimating such effects. Further efforts are needed to verify and elucidate the potential roles of EFNB1/PJA1, KLHL4, TBX22, CPXCR1 and BCOR in isolated clefts.

Comprehensive Expression Profiling and Functional Network Analysis of Porphyra-334, One Mycosporine-Like Amino Acid (MAA), in Human Keratinocyte Exposed with UV-radiation

Mycosporine-like amino acids (MAAs) have been highlighted as pharmacologically active secondary compounds to protect cells from harmful UV-radiation by absorbing its energy. Previous studies have mostly focused on characterizing their physiological properties such as antioxidant activity and osmotic regulation. However, molecular mechanisms underlying their UV-protective capability have not yet been revealed. In the present study, we investigated the expression profiling of porphyra-334-modulated genes or microRNA (miRNAs) in response to UV-exposure and their functional networks, using cDNA and miRNAs microarray. Based on our data, we showed that porphyra-334-regulated genes play essential roles in UV-affected biological processes such as Wnt (Wingless/integrase-1) and Notch pathways which exhibit antagonistic relationship in various biological processes; the UV-repressed genes were in the Wnt signaling pathway, while the activated genes were in the Notch signaling. In addition, porphyra-334-regulated miRNAs can target many genes related with UV-mediated biological processes such as apoptosis, cell proliferation and translational elongation. Notably, we observed that functional roles of the target genes for up-regulated miRNAs are inversely correlated with those for down-regulated miRNAs; the former genes promote apoptosis and translational elongation, whereas the latter function as inhibitors in these processes. Taken together, these data suggest that porphyra-334 protects cells from harmful UV radiation through the comprehensive modulation of expression patterns of genes involved in UV-mediated biological processes, and that provide a new insight to understand its functional molecular networks.

Xenopus as a model organism for birth defects-Congenital heart disease and heterotaxy

Congenital heart disease is the leading cause of birth defects, affecting 9 out of 1000 newborns each year. A particularly severe form of congenital heart disease is heterotaxy, a disorder of left-right development. Despite aggressive surgical management, patients with heterotaxy have poor survival rates and severe morbidity due to their complex congenital heart disease. Recent genetic analysis of affected patients has found novel candidate genes for heterotaxy although their underlying mechanisms remain unknown. In this review, we discuss the importance and challenges of birth defects research including high locus heterogeneity and few second alleles that make defining disease causality difficult. A powerful strategy moving forward is to analyze these candidate genes in a high-throughput human disease model. Xenopus is ideal for these studies. We present multiple examples demonstrating the power of Xenopus in discovering new biology from the analysis of candidate heterotaxy genes such as GALNT11, NEK2 and BCOR. These genes have diverse roles in embryos and have led to a greater understanding of complex signaling pathways and basic developmental biology. It is our hope that the mechanistic analysis of these candidate genes in Xenopus enabled by next generation sequencing of patients will provide clinicians with a greater understanding of patient pathophysiology allowing more precise and personalized medicine, to help patients more effectively in the future.

Pulmonary Agenesis and Associated Pulmonary Hypertension: A Case Report and Review on Variability, Therapy, and Outcome

Pulmonary agenesis is a rare congenital disorder with large variability in presentation and prognosis. We describe a full-term infant born with right-sided pulmonary agenesis who underwent thoracoscopic placement of a tissue expander. He ultimately died of pulmonary hypertension. Immunohistology showed intimal hyperplasia without the loss of endothelial caveolin-1 expression. A literature review revealed that while some of these patients have favorable outcome, many succumb despite therapy.