<em>Xenopus</em> Reduced Folate Carrier Regulates Neural Crest Development Epigenetically

Folic acid deficiency during pregnancy causes birth neurocristopathic malformations resulting from aberrant development of neural crest cells. The Reduced folate carrier (RFC) is a membrane-bound receptor for facilitating transfer of reduced folate into the cells. RFC knockout mice are embryonic lethal and develop multiple malformations, including neurocristopathies. Here we show that XRFC is specifically expressed in neural crest tissues in Xenopus embryos and knockdown of XRFC by specific morpholino results in severe neurocristopathies. Inhibition of RFC blocked the expression of a series of neural crest marker genes while overexpression of RFC or injection of 5-methyltetrahydrofolate expanded the neural crest territories. In animal cap assays, knockdown of RFC dramatically reduced the mono- and trimethyl-Histone3-K4 levels and co-injection of the lysine methyltransferase hMLL1 largely rescued the XRFC morpholino phenotype. Our data revealed that the RFC mediated folate metabolic pathway likely potentiates neural crest gene expression through epigenetic modifications.妊娠期间的叶酸缺乏可引发因神经嵴细胞发育异常导致的神经嵴病性先天畸形。还原型叶酸载体（Reduced folate carrier, RFC）是一类膜结合受体，可介导还原型叶酸向细胞内转运。RFC敲除小鼠存在胚胎致死表型，并会出现包括神经嵴病在内的多种畸形。本研究证实，非洲爪蟾胚胎中的XRFC仅在神经嵴组织中特异性表达；通过特异性吗啉代寡核苷酸敲低XRFC，会引发严重的神经嵴病表型。抑制RFC功能会阻断一系列神经嵴标记基因的表达，而过表达RFC或注射5-甲基四氢叶酸则可扩大神经嵴的区域范围。在动物帽实验中，敲低RFC会显著降低组蛋白H3赖氨酸4的单甲基化和三甲基化水平；共注射赖氨酸甲基转移酶hMLL1，则可大幅挽救XRFC敲低所引发的表型。本研究结果表明，RFC介导的叶酸代谢通路可能通过表观遗传修饰调控神经嵴基因的表达。