Project description:Orofacial clefts are the most common form of congenital craniofacial malformations worldwide. The etiology of these birth defects is multifactorial, involving genetic and environmental factors. In most cases, however, the underlying causes remain unexplained, precluding molecular understanding of disease mechanisms. Here, we integrated genome-wide association data, targeted re-sequencing of case and control cohorts, cell type-specific epigenomic profiling, and genome architecture analyses, to functionally and molecularly dissect a genomic locus associated with an increased risk of non-syndromic orofacial cleft. We found that common and rare risk variants associated with orofacial cleft intersect with a conserved enhancer (e2p24.2) that becomes activated in cranial neural crest cells—the embryonic cell type responsible for sculpting the craniofacial complex. We mapped e2p24.2 long-range interactions to a topologically associated domain harboring MYCN and DDX1 and demonstrated that both MYCN and DDX1 are required for craniofacial development in chicken embryos. Molecularly, we found that e2p24.2 regulates the expression of MYCN, but not DDX1, in cranial neural crest cells. In turn, DDX1 is a target of the MYC family of transcription factors and a component of the tRNA splicing complex. The loss of DDX1 in cranial neural crest cells resulted in the accumulation of unspliced tRNA fragments, and impaired both global protein synthesis and cranial neural crest cell migration. We further showed that the induction of tRNA fragments is sufficient to disrupt craniofacial development. Together, these results uncovered a molecular mechanism in which impaired tRNA splicing, and the concomitant accumulation of tRNA fragments, affect neural crest and craniofacial development and positioned MYCN, DDX1, and tRNA processing defects as risk factors in the pathogenesis of orofacial clefts.
Project description:Orofacial clefts are the most common form of congenital craniofacial malformations worldwide. The etiology of these birth defects is multifactorial, involving genetic and environmental factors. In most cases, however, the underlying causes remain unexplained, precluding molecular understanding of disease mechanisms. Here, we integrated genome-wide association data, targeted re-sequencing of case and control cohorts, cell type-specific epigenomic profiling, and genome architecture analyses, to functionally and molecularly dissect a genomic locus associated with an increased risk of non-syndromic orofacial cleft. We found that common and rare risk variants associated with orofacial cleft intersect with a conserved enhancer (e2p24.2) that becomes activated in cranial neural crest cells—the embryonic cell type responsible for sculpting the craniofacial complex. We mapped e2p24.2 long-range interactions to a topologically associated domain harboring MYCN and DDX1 and demonstrated that both MYCN and DDX1 are required for craniofacial development in chicken embryos. Molecularly, we found that e2p24.2 regulates the expression of MYCN, but not DDX1, in cranial neural crest cells. In turn, DDX1 is a target of the MYC family of transcription factors and a component of the tRNA splicing complex. The loss of DDX1 in cranial neural crest cells resulted in the accumulation of unspliced tRNA fragments, and impaired both global protein synthesis and cranial neural crest cell migration. We further showed that the induction of tRNA fragments is sufficient to disrupt craniofacial development. Together, these results uncovered a molecular mechanism in which impaired tRNA splicing, and the concomitant accumulation of tRNA fragments, affect neural crest and craniofacial development and positioned MYCN, DDX1, and tRNA processing defects as risk factors in the pathogenesis of orofacial clefts.
Project description:Orofacial clefts are the most common form of congenital craniofacial malformations worldwide. The etiology of these birth defects is multifactorial, involving genetic and environmental factors. In most cases, however, the underlying causes remain unexplained, precluding molecular understanding of disease mechanisms. Here, we integrated genome-wide association data, targeted re-sequencing of case and control cohorts, cell type-specific epigenomic profiling, and genome architecture analyses, to functionally and molecularly dissect a genomic locus associated with an increased risk of non-syndromic orofacial cleft. We found that common and rare risk variants associated with orofacial cleft intersect with a conserved enhancer (e2p24.2) that becomes activated in cranial neural crest cells—the embryonic cell type responsible for sculpting the craniofacial complex. We mapped e2p24.2 long-range interactions to a topologically associated domain harboring MYCN and DDX1 and demonstrated that both MYCN and DDX1 are required for craniofacial development in chicken embryos. We found that e2p24.2 regulates the expression of MYCN, but not DDX1, in cranial neural crest cells. In turn, DDX1 is a target of the MYC family of transcription factors and a component of the tRNA splicing complex. The loss of DDX1 in cranial neural crest cells resulted in the accumulation of unspliced tRNA fragments, depletion of the mature pool of intron-containing tRNAs, and ribosome stalling at codons decoded by these tRNAs. These effects were accompanied by defects in both global protein synthesis and cranial neural crest cell migration. We further showed that the induction of tRNA fragments is sufficient to disrupt craniofacial development. Together, these results uncovered a molecular mechanism in which impaired tRNA splicing affects neural crest and craniofacial development and positioned MYCN, DDX1, and tRNA processing defects as risk factors in the pathogenesis of orofacial clefts.
Project description:Orofacial clefts of the lip and palate are widely recognized to result from complex gene–environment interactions, but inadequate understanding of environmental risk factors has stymied development of prevention strategies. We interrogated the role of DNA methylation, an environmentally malleable epigenetic mechanism, in orofacial development. Expression of the key DNA methyltransferase enzyme DNMT1 was detected throughout palate morphogenesis in the epithelium and underlying cranial neural crest cell (cNCC) mesenchyme, a highly proliferative multipotent stem cell population that forms orofacial connective tissue. Genetic and pharmacologic manipulations of DNMT activity were then applied to define the tissue- and timing-dependent requirement of DNA methylation in orofacial development. cNCC-specific Dnmt1 inactivation targeting initial palate outgrowth resulted in OFCs, while later targeting during palatal shelf elevation and elongation did not. Conditional Dnmt1 deletion reduced cNCC proliferation and subsequent differentiation trajectory, resulting in attenuated outgrowth of the palatal shelves and altered development of cNCC-derived skeletal elements. Finally, we found that the cellular mechanisms of cleft pathogenesis observed in vivo can be recapitulated by pharmacologically reducing DNA methylation in multipotent cNCCs cultured in vitro. These findings demonstrate that DNA methylation is a crucial epigenetic regulator of cNCC biology, define a critical period of development in which its disruption directly causes OFCs, and provide opportunities to identify environmental influences that contribute to OFC risk.