Necdin, a Prader-Willi syndrome candidate gene, regulates gonadotropin-releasing hormone neurons during development

Prader-Willi syndrome (PWS) is a complex genetic disorder characterized by hyperphagia, obesity and hypogonadotrophic hypogonadism, all highly suggestive of hypothalamic dysfunction. The NDN gene, encoding the MAGE family protein, necdin, maps to the PWS chromosome region and is highly expressed in mature hypothalamic neurons. Adult mice lacking necdin have reduced numbers of gonadotropin-releasing hormone (GnRH) neurons, but the mechanism for this reduction is unknown. Herein, we show that, although necdin is not expressed in an immature, migratory GnRH neuronal cell line (GN11), high levels are present in a mature GnRH neuronal cell line (GT1-7). Furthermore, overexpression of necdin activates GnRH transcription through cis elements bound by the homeodomain repressor Msx that are located in the enhancer and promoter of the GnRH gene, and knock-down of necdin expression reduces GnRH gene expression. In fact, overexpression of Necdin relieves Msx repression of GnRH transcription through these elements and necdin co-immunoprecipitates with Msx from GnRH neuronal cells, indicating that necdin may activate GnRH gene expression by preventing repression of GnRH gene expression by Msx. Finally, necdin is necessary for generation of the full complement of GnRH neurons during mouse development and extension of GnRH axons to the median eminence. Together, these results indicate that lack of necdin during development likely contributes to the hypogonadotrophic hypogonadal phenotype in individuals with PWS.

普拉德 - 威利综合征（PWS）是一种复杂的遗传性疾病，其特征为多食、肥胖和低促性腺激素性性腺功能减退，所有这些都高度提示下丘脑功能障碍。编码MAGE家族蛋白necdin的NDN基因定位于PWS染色体区域，且在成熟的下丘脑神经元中高度表达。缺乏necdin的成年小鼠促性腺激素释放激素（GnRH）神经元数量减少，但这种减少的机制尚不清楚。在此，我们表明，尽管necdin在未成熟的迁移性GnRH神经元细胞系（GN11）中不表达，但在成熟的GnRH神经元细胞系（GT1 - 7）中大量存在。此外，necdin的过表达通过位于GnRH基因增强子和启动子中由同源结构域抑制因子Msx结合的顺式元件激活GnRH转录，并且necdin表达的敲低会降低GnRH基因表达。事实上，Necdin的过表达通过这些元件解除了Msx对GnRH转录的抑制，并且necdin与来自GnRH神经元细胞的Msx共免疫沉淀，这表明necdin可能通过阻止Msx对GnRH基因表达的抑制来激活GnRH基因表达。最后，necdin对于小鼠发育过程中GnRH神经元的完全补充以及GnRH轴突延伸至正中隆起是必需的。总之，这些结果表明，发育过程中necdin的缺乏可能导致PWS患者的低促性腺激素性性腺功能减退表型。