Gene-environment interactions in rare diseases that include common birth defects

AbstractGene-environment interactions are likely to underlie most human birth defects. The most common environmental contributor to birth defects is likely prenatal alcohol exposure. Fetal Alcohol Spectrum Disorders (FASD) describes the full range of defects that result from prenatal alcohol exposure. Gene-ethanol interactions underlie susceptibility to FASD but we lack a mechanistic understanding of these interactions. Here, we leverage the genetic tractability of zebrafish to address this problem. We first show that vangl2, a member of the Wnt/planar cell polarity (Wnt/PCP) pathway that mediates convergent extension movements, strongly interacts with ethanol during late blastula and early gastrula stages. Embryos mutant or heterozygous for vangl2 are sensitized to ethanol- induced midfacial hypoplasia. We performed single-embryo RNA-Seq during early embryonic stages, to assess individual variation to the transcriptional response to ethanol and determine the mechanism of the vangl2-ethanol interaction. To identify the pathway(s) that are disrupted by ethanol we used these global changes in gene expression to identify small molecules that mimic the effects of ethanol via the Library of Integrated Network- based Cellular Signatures (LINCS L1000) dataset. Surprisingly, this dataset predicted that the Sonic Hedgehog (Shh) pathway inhibitor, cyclopamine, would mimic the effects of ethanol, despite the fact that ethanol did not alter the expression levels of direct targets of Shh signaling. Indeed, we found that ethanol and cyclopamine strongly interact to disrupt midfacial development. Collectively, these results suggest that the midfacial defects in ethanol-exposed vangl2 mutants are due to an indirect interaction between ethanol and the Shh pathway. Vangl2 functions as part of a signaling pathway that regulates coordinated cell movements during midfacial development. Consistent with an indirect model, a critical source of Shh signaling that separates the developing eye field into bilateral eyes, allowing the expansion of the midface, becomes mispositioned in ethanol-exposed vangl2 mutants. We demonstrate that ethanol also interacts with another Wnt/PCP pathway member, gpc4, and a chemical inhibitor, blebbistatin. By characterizing membrane protrusions, we demonstrate that ethanol synergistically interacts with the loss of vangl2 to disrupt cell polarity required for convergent extension movements. Collectively, our results shed light on the mechanism by which the most common teratogen can disrupt development.

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Gene Environment Interactions in the Etiology of Neural Tube Defects

Frontiers in Genetics ◽

10.3389/fgene.2021.659612 ◽

2021 ◽

Vol 12 ◽

Author(s):

Richard H. Finnell ◽

Carlo Donato Caiaffa ◽

Sung-Eun Kim ◽

Yunping Lei ◽

John Steele ◽

...

Keyword(s):

United States ◽

Folic Acid ◽

Spina Bifida ◽

Birth Defects ◽

Neural Tube ◽

Neural Tube Defects ◽

The United States ◽

Model Systems ◽

Posterior Portion ◽

Gene Environment

Human structural congenital malformations are the leading cause of infant mortality in the United States. Estimates from the United States Center for Disease Control and Prevention (CDC) determine that close to 3% of all United States newborns present with birth defects; the worldwide estimate approaches 6% of infants presenting with congenital anomalies. The scientific community has recognized for decades that the majority of birth defects have undetermined etiologies, although we propose that environmental agents interacting with inherited susceptibility genes are the major contributing factors. Neural tube defects (NTDs) are among the most prevalent human birth defects and as such, these malformations will be the primary focus of this review. NTDs result from failures in embryonic central nervous system development and are classified by their anatomical locations. Defects in the posterior portion of the neural tube are referred to as meningomyeloceles (spina bifida), while the more anterior defects are differentiated as anencephaly, encephalocele, or iniencephaly. Craniorachischisis involves a failure of the neural folds to elevate and thus disrupt the entire length of the neural tube. Worldwide NTDs have a prevalence of approximately 18.6 per 10,000 live births. It is widely believed that genetic factors are responsible for some 70% of NTDs, while the intrauterine environment tips the balance toward neurulation failure in at risk individuals. Despite aggressive educational campaigns to inform the public about folic acid supplementation and the benefits of providing mandatory folic acid food fortification in the United States, NTDs still affect up to 2,300 United States births annually and some 166,000 spina bifida patients currently live in the United States, more than half of whom are now adults. Within the context of this review, we will consider the role of maternal nutritional status (deficiency states involving B vitamins and one carbon analytes) and the potential modifiers of NTD risk beyond folic acid. There are several well-established human teratogens that contribute to the population burden of NTDs, including: industrial waste and pollutants [e.g., arsenic, pesticides, and polycyclic aromatic hydrocarbons (PAHs)], pharmaceuticals (e.g., anti-epileptic medications), and maternal hyperthermia during the first trimester. Animal models for these teratogens are described with attention focused on valproic acid (VPA; Depakote). Genetic interrogation of model systems involving VPA will be used as a model approach to discerning susceptibility factors that define the gene-environment interactions contributing to the etiology of NTDs.

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