Previously, we reported global hypermethylation in DS might be attributed to the overexpression of HSA21 gene DNMT3L, which can enhance DNMT3A and DNMT3B activities in DNA methylation. To test this hypothesis, we compared the DNA methylation and RNA expression profiles of early-differentiated human neuroprogenitors with and without DNMT3L overexpression. We found DNMT3L overexpression only moderately increased the DNA methylation of limited genes, yet significantly altered global RNA expression of genes involved in neural differentiation. We further found that DNMT3L bound STAT1 or STAT3, and increased its phosphorylation and nuclear translocation, which in turn activated the expression of transcription factors including HES3, ASCL1, NEUROD2 and NEUROG2 and CDK inhibitor CDKN1A, which promoted cell cycle exit and neural differentiation. This phenomenon was also confirmed in Dnmt3l conditional knockin mice, which could be rescued by STAT1 and STAT3 phosphorylation inhibitors (Fludarabine and SH-4−54) but not DNA methylation inhibitor (Decitabine). These results suggest that DNMT3L play an important role during neurodevelopment independent of DNA methylation, which may contribute to the abnormal phenotypes observed in Down syndrome cortex.

以前，我们报道了 DS 中的全局高甲基化可能归因于 HSA21 基因DNMT3L的过表达，可增强 DNMT3A 和 DNMT3B 在 DNA 甲基化中的活性。为了检验这一假设，我们比较了有和没有 DNMT3L 过表达的早期分化人类神经祖细胞的 DNA 甲基化和 RNA 表达谱。我们发现 DNMT3L 过表达仅适度增加了有限基因的 DNA 甲基化，但显着改变了参与神经分化的基因的全局 RNA 表达。我们进一步发现DNMT3L与STAT1或STAT3结合，增加其磷酸化和核转位，进而激活包括HES3、ASCL1、NEUROD2和NEUROG2在内的转录因子和CDK抑制剂CDKN1A的表达，从而促进细胞周期退出和神经分化。这种现象在Dnmt3l中也得到了证实条件性敲入小鼠，可由 STAT1 和 STAT3 磷酸化抑制剂（氟达拉滨和 SH-4-54）拯救，但不能通过 DNA 甲基化抑制剂（地西他滨）拯救。这些结果表明，DNMT3L 在独立于 DNA 甲基化的神经发育过程中发挥重要作用，这可能导致在唐氏综合征皮质中观察到的异常表型。