Cariboni Anna, Hickok Jason, Rakic Sonja, Andrews William, Maggi Roberto, Tischkau Shelley, Parnavelas John G
Department of Anatomy and Developmental Biology, University College London, London WC1E 6BT, United Kingdom.
J Neurosci. 2007 Feb 28;27(9):2387-95. doi: 10.1523/JNEUROSCI.5075-06.2007.
Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus play an important role in reproductive function. These cells originate in the nasal compartment and migrate into the basal forebrain in association with olfactory/vomeronasal nerves in embryonic life in rodents. Here, we studied the role of neuropilins and their ligands, semaphorins, in the development of the olfactory-GnRH system. We focused on Neuropilin-2 knock-out (Npn-2(-/-)) mice, because they are known to display defasciculation of olfactory nerves and reduced fertility. We found a significant decrease in the number of GnRH neurons in the hypothalamus and a marked reduction in their gonadal size. We then observed an abnormal increase of GnRH neurons in the noses of Npn-2(-/-) mice, indicating that these cells failed to migrate into the forebrain. However, because neuropilins and semaphorins are involved in events of neuronal migration in the brain, we asked whether the observed reduction in GnRH neurons was directly attributable to the action of these molecules. Using fluorescence-activated cell sorting and reverse transcription-PCR on mRNA derived from embryonic green fluorescent protein (GFP)-GnRH transgenic mice, we found expression of class 3 semaphorins and their receptors (neuropilin-1/2 and plexin-A1) in GnRH neurons. Furthermore, double-immunofluorescence experiments showed that migrating GnRH neurons, as well as associated olfactory fibers, express Npn-2 in the nasal region. We then used a line of immortalized GnRH neurons (GN11 cells) that display the same expression patterns for semaphorins and their receptors as GFP-GnRH cells and found that class 3 semaphorins and vascular endothelial growth factors modulate their migratory activity. These studies provide support for the direct involvement of neuropilins and their ligands in the establishment of the GnRH neuroendocrine system.
下丘脑促性腺激素释放激素（GnRH）神经元在生殖功能中起重要作用。这些细胞起源于鼻腔区域，并在啮齿动物胚胎期与嗅神经/犁鼻神经一起迁移至基底前脑。在此，我们研究了神经纤毛蛋白及其配体（信号素）在嗅觉 - GnRH系统发育中的作用。我们聚焦于神经纤毛蛋白2基因敲除（Npn - 2(-/-)）小鼠，因为已知它们表现出嗅神经解束和生育力降低。我们发现下丘脑GnRH神经元数量显著减少，其性腺大小明显减小。然后我们观察到Npn - 2(-/-)小鼠鼻腔中GnRH神经元异常增多，表明这些细胞未能迁移至前脑。然而，由于神经纤毛蛋白和信号素参与大脑中神经元迁移事件，我们询问观察到GnRH神经元数量减少是否直接归因于这些分子的作用。通过对源自胚胎绿色荧光蛋白（GFP） - GnRH转基因小鼠的mRNA进行荧光激活细胞分选和逆转录 - PCR，我们发现GnRH神经元中表达3类信号素及其受体（神经纤毛蛋白 - 1/2和丛蛋白 - A1）。此外，双重免疫荧光实验表明，迁移的GnRH神经元以及相关的嗅纤维在鼻腔区域表达Npn - 2。然后我们使用了永生化的GnRH神经元系（GN11细胞），其信号素及其受体的表达模式与GFP - GnRH细胞相同，发现3类信号素和血管内皮生长因子调节它们的迁移活性。这些研究为神经纤毛蛋白及其配体直接参与GnRH神经内分泌系统的建立提供了支持。
