Hoffmann Hanne M, Trang Crystal, Gong Ping, Kimura Ikuo, Pandolfi Erica C, Mellon Pamela L
Department of Reproductive Medicine and the Center for Reproductive Science and Medicine, University of California, San Diego, La Jolla, California 92093-0674, and.
Department of Applied Biological Science, Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Fuchu-shi 183-8509, Japan.
J Neurosci. 2016 Mar 23;36(12):3506-18. doi: 10.1523/JNEUROSCI.2723-15.2016.
Hypothalamic gonadotropin-releasing hormone (GnRH) neurons are at the apex of the hypothalamic-pituitary-gonadal axis that regulates mammalian fertility. Herein we demonstrate a critical role for the homeodomain transcription factor ventral anterior homeobox 1 (VAX1) in GnRH neuron maturation and show that Vax1 deletion from GnRH neurons leads to complete infertility in males and females. Specifically, global Vax1 knock-out embryos had normal numbers of GnRH neurons at 13 d of gestation, but no GnRH staining was detected by embryonic day 17. To identify the role of VAX1 specifically in GnRH neuron development,Vax1(flox)mice were generated and lineage tracing performed in Vax1(flox/flox):GnRH(cre):RosaLacZ mice. This identified VAX1 as essential for maintaining expression of Gnrh1 The absence of GnRH staining in adult Vax1(flox/flox):GnRH(cre)mice led to delayed puberty, hypogonadism, and infertility. To address the mechanism by which VAX1 maintains Gnrh1 transcription, the capacity of VAX1 to regulate Gnrh1 transcription was evaluated in the GnRH cell lines GN11 and GT1-7. As determined by luciferase and electrophoretic mobility shift assays, we found VAX1 to be a direct activator of the GnRH promoter through binding to four ATTA sites in the GnRH enhancer (E1) and proximal promoter (P), and able to compete with the homeoprotein SIX6 for occupation of the identified ATTA sites in the GnRH promoter. We conclude that VAX1 is expressed in GnRH neurons where it is required for GnRH neuron expression of GnRH and maintenance of fertility in mice.
Infertility classified as idiopathic hypogonadotropic hypogonadism (IHH) is characterized by delayed or absent sexual maturation and low sex steroid levels due to alterations in neuroendocrine control of the hypothalamic-pituitary-gonadal axis. The incidence of IHH is 1-10 cases per 100,000 births. Although extensive efforts have been invested in identifying genes giving rise to IHH, >50% of cases have unknown genetic origins. We recently showed that haploinsufficiency of ventral anterior homeobox 1 (Vax1) leads to subfertility, making it a candidate in polygenic IHH. In this study, we investigate the mechanism by which VAX1 controls fertility finding that VAX1 is required for maintenance of Gnrh1 gene expression and deletion of Vax1 from GnRH neurons leads to complete infertility.
下丘脑促性腺激素释放激素（GnRH）神经元位于调节哺乳动物生育能力的下丘脑-垂体-性腺轴的顶端。在此，我们证明了同源结构域转录因子腹侧前同源框1（VAX1）在GnRH神经元成熟中起关键作用，并表明从GnRH神经元中删除Vax1会导致雄性和雌性完全不育。具体而言，在妊娠13天时，全局Vax1基因敲除胚胎的GnRH神经元数量正常，但在胚胎第17天时未检测到GnRH染色。为了确定VAX1在GnRH神经元发育中的具体作用，我们构建了Vax1（flox）小鼠，并在Vax1（flox/flox）：GnRH（cre）：RosaLacZ小鼠中进行了谱系追踪。这确定了VAX1对于维持Gnrh1的表达至关重要。成年Vax1（flox/flox）：GnRH（cre）小鼠中缺乏GnRH染色导致青春期延迟、性腺功能减退和不育。为了探究VAX1维持Gnrh1转录的机制，我们在GnRH细胞系GN11和GT1-7中评估了VAX1调节Gnrh1转录的能力。通过荧光素酶和电泳迁移率变动分析确定，我们发现VAX1通过与GnRH增强子（E1）和近端启动子（P）中的四个ATTA位点结合，是GnRH启动子的直接激活剂，并且能够与同源蛋白SIX6竞争占据GnRH启动子中已确定的ATTA位点。我们得出结论，VAX1在GnRH神经元中表达，在小鼠中它是GnRH神经元表达GnRH和维持生育能力所必需的。
被归类为特发性低促性腺激素性性腺功能减退（IHH）的不孕症的特征是由于下丘脑-垂体-性腺轴神经内分泌控制的改变导致性成熟延迟或缺失以及性类固醇水平低下。IHH的发病率为每10万例出生中有1-10例。尽管已经投入大量精力来鉴定导致IHH的基因，但超过50%的病例的遗传起源尚不清楚。我们最近表明，腹侧前同源框1（Vax1）的单倍体不足会导致生育力低下，使其成为多基因IHH的一个候选基因。在本研究中，我们研究了VAX1控制生育力的机制，发现VAX1是维持Gnrh1基因表达所必需的，并且从GnRH神经元中删除Vax1会导致完全不育。
