Department of Biological Sciences, Kent State University, Kent, Ohio, United States of America.
School of Biomedical Sciences, Kent State University, Kent, Ohio, United States of America.
PLoS One. 2019 Jul 30;14(7):e0220530. doi: 10.1371/journal.pone.0220530. eCollection 2019.
Fibroblast growth factor 8 (FGF8) is a potent morphogen that regulates the ontogenesis of gonadotropin-releasing hormone (GnRH) neurons, which control the hypothalamus-pituitary-gonadal (HPG) axis, and therefore reproductive success. Indeed, FGF8 and FGFR1 deficiency severely compromises vertebrate reproduction in mice and humans and is associated with Kallmann Syndrome (KS), a congenital disease characterized by hypogonadotropic hypogonadism associated with anosmia. Our laboratory demonstrated that FGF8 signaling through FGFR1, both of which are KS-related genes, is necessary for proper GnRH neuron development in mice and humans. Here, we investigated the possibility that non-genetic factors, such as the epigenome, may contribute to KS onset. For this purpose, we developed an embryonic explant model, utilizing the mouse olfactory placode (OP), the birthplace of GnRH neurons. We show that TET1, which converts 5-methylcytosine residues (5mC) to 5-hydroxymethylated cytosines (5hmC), controls transcription of Fgf8 during GnRH neuron ontogenesis. Through MeDIP and ChIP RT-qPCR we found that TET1 bound to specific CpG islands on the Fgf8 promoter. We found that the temporal expression of Fgf8 correlates with not only TET1 binding, but also with 5hmC enrichment. siRNA knockdown of Tet1 reduced Fgf8 and Fgfr1 mRNA expression. During this time period, Fgf8 also switched histone status, most likely via recruitment of EZH2, a major component of the polycomb repressor complex-2 (PRC2) at E13.5. Together, these studies underscore the significance of epigenetics and chromatin modifications to temporally regulated genes involved in KS.
成纤维细胞生长因子 8（FGF8）是一种有效的形态发生因子，可调节促性腺激素释放激素（GnRH）神经元的个体发生，后者控制下丘脑-垂体-性腺（HPG）轴，从而控制生殖成功。实际上，FGF8 和 FGFR1 的缺乏严重损害了小鼠和人类的脊椎动物繁殖能力，并与 Kallmann 综合征（KS）相关，KS 是一种先天性疾病，其特征是促性腺激素低下性性腺功能减退症伴嗅觉缺失。我们的实验室证明，FGF8 通过 FGFR1 的信号传导（这两者都是 KS 相关基因）对于小鼠和人类中 GnRH 神经元的正常发育是必需的。在这里，我们研究了非遗传因素（例如表观基因组）是否可能导致 KS 发作的可能性。为此，我们开发了一种胚胎外植体模型，利用了小鼠嗅觉基板（OP），即 GnRH 神经元的发源地。我们表明，TET1 将 5-甲基胞嘧啶残基（5mC）转化为 5-羟甲基胞嘧啶（5hmC），可控制 GnRH 神经元个体发生过程中 Fgf8 的转录。通过 MeDIP 和 ChIP RT-qPCR，我们发现 TET1 结合到 Fgf8 启动子上的特定 CpG 岛。我们发现 Fgf8 的时空表达不仅与 TET1 结合，而且与 5hmC 富集相关。Tet1 的 siRNA 敲低降低了 Fgf8 和 Fgfr1 mRNA 的表达。在此期间，Fgf8 还改变了组蛋白状态，很可能通过募集 EZH2 来实现，EZH2 是多梳抑制复合物 2（PRC2）的主要成分之一，在 E13.5 时被募集。综上所述，这些研究强调了表观遗传学和染色质修饰对参与 KS 的时空调节基因的重要性。
