Synaptophysin (Syp) is an integral membrane protein of synaptic vesicles, and is ubiquitously expressed in neurons throughout the brain. As Syp expression is correlated with synaptogenesis during development of the central nervous system, the expression of Syp is considered to be a critical aspect of neuronal maturation and circuit formation. However, little information is available concerning the regulatory mechanisms of Syp gene expression during postnatal development of the brain. In the present study, we investigated changes in Syp mRNA in the hippocampus of mice during postnatal development, and examined the gene regulation mechanisms, focusing on DNA methylation. We found that hippocampal Syp expression involving both mRNA and protein levels increased during the first two weeks of life, and that this increase was accompanied by a transition from hypermethylation to hypomethylation at the CpG sites of the Syp gene upstream region. In addition, DNA demethylating agent 5-Aza-2'-deoxycytidine (5-aza-dC) de-repressed Syp gene expression both in vitro in Neuro-2a mouse neuronal cells and in vivo in the hippocampus of early postnatal mice. Furthermore, the methylation levels at upstream region of Syp gene in the hippocampus of developing mice was decreased by intraperitoneal injection of 5-aza-dC. These results suggest that Syp gene regulation, at least during postnatal brain development, could be mediated by DNA methylation. Our findings promote understanding of the molecular basis of synaptogenesis during postnatal brain development, and provide novel insight into therapeutic aspects of neurodevelopmental disorders involving synaptic dysfunction.

中文翻译：

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小鼠出生后发育过程中DNA甲基化可能与海马突触素基因表达有关。

突触素（Syp）是突触小泡的必不可少的膜蛋白，在整个大脑的神经元中普遍表达。由于Syp的表达与中枢神经系统发育过程中的突触发生相关，因此Syp的表达被认为是神经元成熟和回路形成的关键方面。但是，关于大脑产后发育过程中Syp基因表达调控机制的信息很少。在本研究中，我们调查了出生后小鼠海马中Syp mRNA的变化，并研究了基因调控机制，重点是DNA甲基化。我们发现，在生命的前两周，涉及mRNA和蛋白质水平的海马Syp表达增加，而且这种增加伴随着Syp基因上游区域CpG位点从高甲基化到低甲基化的转变。此外，DNA脱甲基剂5-Aza-2'-脱氧胞苷（5-aza-dC）在Neuro-2a小鼠神经元细胞的体外和体内在出生后早期小鼠的海马中均能抑制Syp基因的表达。此外，腹膜内注射5-氮杂-dC可以降低发育中小鼠海马中Syp基因上游区域的甲基化水平。这些结果表明，至少在产后大脑发育过程中，Syp基因调控可能是由DNA甲基化介导的。我们的发现促进了对产后大脑发育过程中突触形成的分子基础的理解，