Izvolskaia Marina, Duittoz Anne H, Ugrumov Mikhail V, Tillet Yves
Laboratory of Hormonal Regulations, Institute of Developmental Biology, Russian Academy of Sciences, Vavilov str., 26,119991 Moscow, Russia.
Brain Res. 2006 Apr 14;1083(1):29-38. doi: 10.1016/j.brainres.2006.01.130. Epub 2006 Mar 23.
Transient expression of tyrosine hydroxylase (TH, the first enzyme in catecholamine synthesis) has been shown in different brain and peripheral structures of various species. TH-immunoreactive neurons have been reported in the nasal region of human and rat fetuses migrating to the forebrain with GnRH neurons during embryogenesis. In the present study, immunohistochemical analysis and in situ hybridization were performed in fetal sheep and in vitro sheep embryo olfactory placode cultures to confirm this population in this species. On embryonic days 33 to 35, TH-immunoreactive cells as well as TH cDNA-hybridized cells were found in the olfactory and respiratory epithelium and were spatially separated from GnRH-immunoreactive neurons. In days 40 to 44 of gestation, TH-immunoreactive neurons were no longer observed in the olfactory epithelium, and TH-immunoreactive fibers were found on the trajectories of the olfactory nerves. At this stage, some TH-immunoreactive fibers were also labeled for GnRH. TH-immunoreactive cells were also found in primary cultures of olfactory placodes of fetal sheep at 10 to 18 days in vitro. Some of them coexpressed GnRH. These results imply that olfactory epithelium is also able to give rise to TH expressing cells in fetal sheep, but this expression is suppressed earlier in ontogenesis than in humans due to some unidentified factors not present in the primary cultures of olfactory placode. The role of TH expression remains unclear as in other previously described examples.
酪氨酸羟化酶（TH，儿茶酚胺合成的第一种酶）的瞬时表达已在不同物种的不同脑区和外周结构中得到证实。据报道，在胚胎发育过程中，人类和大鼠胎儿的鼻腔区域存在TH免疫反应性神经元，它们与促性腺激素释放激素（GnRH）神经元一起迁移至前脑。在本研究中，对胎羊和体外培养的羊胚胎嗅基板进行了免疫组织化学分析和原位杂交，以确认该物种中的这一细胞群体。在胚胎第33至35天，在嗅觉和呼吸上皮中发现了TH免疫反应性细胞以及TH cDNA杂交细胞，它们在空间上与GnRH免疫反应性神经元分离。在妊娠第40至44天，嗅觉上皮中不再观察到TH免疫反应性神经元，而在嗅神经的轨迹上发现了TH免疫反应性纤维。在此阶段，一些TH免疫反应性纤维也被标记为GnRH。在体外培养10至18天的胎羊嗅基板原代培养物中也发现了TH免疫反应性细胞。其中一些细胞共表达GnRH。这些结果表明，嗅上皮在胎羊中也能够产生表达TH的细胞，但由于嗅基板原代培养物中不存在某些未知因素，这种表达在个体发育中比在人类中更早受到抑制。与其他先前描述的例子一样，TH表达的作用仍不清楚。
