Search

Neural tube defects (NTDs) are serious congenital malformations. Excessive maternal homocysteine (Hcy) increases the risk of NTDs, while its mechanism remains elusive. Here we report the role of histone homocysteinylation in neural tube closure (NTC). A total of 39 histone homocysteinylation sites are identified in samples from human embryonic brain tissue using mass spectrometry. Elevated levels of histone KHcy and H3K79Hcy are detected at increased cellular Hcy levels in human fetal brains. Using ChIP-seq and RNA-seq assays, we demonstrate that an increase in H3K79Hcy level down-regulates the expression of selected NTC-related genes including Cecr2, Smarca4, and Dnmt3b. In human NTDs brain tissues, decrease in expression of CECR2, SMARCA4, and DNMT3B is also detected along with high levels of Hcy and H3K79Hcy. Our results suggest that higher levels of Hcy contribute to the onset of NTDs through up-regulation of histone H3K79Hcy, leading to abnormal expressions of selected NTC-related genes. Elevated maternal homocysteine (Hcy) increases the risk for neural tube defects (NTDs) but how this arises is unclear. Here, the authors show that high levels of Hcy on histone H3K79Hcy correlate with NTDs, causing abnormal gene expression (for example Cecr2, Smarca4 and Dnmt3B) linked to neural tube closure. [ABSTRACT FROM AUTHOR]

Neural tube defects (NTDs) are severe malformations of the central nervous system caused by complex genetic and environmental factors. Among genes involved in NTD, cilia-related genes have been well defined and found to be essential for the completion of neural tube closure (NTC). We have carried out next-generation sequencing on target genes in 373 NTDs and 222 healthy controls, and discovered eight disease-specific rare mutations in cilia-related gene DNAAF1 DNAAF1 plays a central role in cytoplasmic preassembly of distinct dynein-arm complexes, and is expressed in some key tissues involved in neural system development, such as neural tube, floor plate, embryonic node, and brain ependyma epithelial cells in zebrafish and mouse. Therefore, we evaluated the expression and functions of mutations in DNAAF1 in transfected cells to analyze the potential correlation of these mutants to NTDs in humans. One rare frameshift mutation (p.Gln341Argfs*10) resulted in significantly diminished DNAAF1 protein expression, compared to the wild type. Another mutation, p.Lys231Gln, disrupted cytoplasmic preassembly of the dynein-arm complexes in cellular assay. Furthermore, results from NanoString assay on mRNA from NTD samples indicated that DNAAF1 mutants altered the expression level of NTC-related genes. Altogether, these findings suggest that the rare mutations in DNAAF1 may contribute to the susceptibility for NTDs in humans., (Copyright © 2016 Miao et al.)

The association between Wnt genes and neural tube defects (NTDs) is recognized, however, it remains to be fully elucidated. Our previous study demonstrated that epigenetic mechanisms are affected in human NTDs. Therefore, the present study aimed to evaluate whether Wnt2b and Wnt7b are susceptible to abnormal epigenetic modification in NTDs, using chromatin immunoprecipitation assays to evaluate histone enrichments and the MassARRAY platform to detect the methylation levels of target regions within Wnt genes. The results demonstrated that the transcriptional activities of Wnt2b and Wnt7b were abnormally upregulated in mouse fetuses with NTDs and, in the GC‑rich promoters of these genes, histone 3 lysine 4 (H3K4) acetylation was enriched, whereas H3K27 trimethylation was reduced. Furthermore, several CpG sites in the altered histone modification of target regions were significantly hypomethylated. The present study also detected abnormal epigenetic modifications of these Wnt genes in human NTDs. In conclusion, the present study detected abnormal upregulation in the levels of Wnt2b and Wnt7b, and hypothesized that the alterations may be due to the ectopic opening of chromatin structure. These results improve understanding of the dysregulation of epigenetic modification of Wnt genes in NTDs.

Birth defects are common, serious malformations with a complex etiology that suggests involvement of both genetic and environmental factors. Low dietary folate and polymorphisms in genes of folate metabolism can influence risk for birth defects. In the present study 250 Chinese birth defects cases who suffered 1-8 types of birth defect disease phenotypes were subjected and two genetic variants in two folate metabolism key enzymes, rs1801394 of methionine synthase reductase (MTRR) and rs1801133 of methylenetetrahydrofolate reductase (MTHFR) were genotyped by using SNaPshot method. The results indicated that rs1801394 and rs1801133 were associated with multiple birth defects. According to homology of organogenesis, the disease phenotypes were classified into ectoderm-, mesoderm-, and endoderm-developed groups. Genetic analysis results displayed that as protective factors, genetic variants of rs1801133 and rs1801394 were associated with the risk of ectoderm-, and endoderm-developed malformations, but only the variant of rs1801394 was associated with the risk of mesoderm-developed malformations. Our present study first related nutrition metabolism related gene variants to germ layers and provided a novel understanding of an implication of earlier causation of birth defects pathogenesis in humans.