Murphy Amy E, Harvey Steve
Department of Physiology, Perinatal Research Centre, University of Alberta, Edmonton, Canada.
J Mol Neurosci. 2002 Feb-Apr;18(1-2):77-87. doi: 10.1385/JMN:18:1-2:77.
The expression of the thyrotropin (TSH) gene in the pituitary gland is thought to be dependent upon the pituitary-specific transcription factor, Pit-1. TSH immunoreactivity is, however, widespread in extrapituitary tissues, and the possibility that this may reflect a widespread distribution of Pit-1 was therefore investigated in embryonic chicks, prior to the ontogenic differentiation of the pituitary gland. TSH immunoreactivity in chick embryos at the end of the first trimester of the 21d incubation period was present in discrete cells in the developing brain (particularly in ependymal cells lining the diocoele and mesocoele and in cells lining the otic vesicle), spinal cord (ependymal cells), liver (hepatocytes), lungs (in the linings of the bronchi), gut (in the linings of the proventriculus) and limb bud (in skin, muscle, bone and nerve fibers). In some of these tissues (particularly in brain and spinal cord ependymal cells, cells in the otic vesicle and in liver hepatocytes), the distribution of TSH immunoreactivity was overlapped by the distribution of immunoreactive Pit-1, suggesting Pit-1 involvement in TSH expression in these sites. However, in other tissues (e.g., the trigeminal nerve in the head and the marginal mantle layer of the spinal cord), Pit-1 immunoreactivity was intense but TSH immunoreactivity was marginal. Conversely, other tissues (e.g., cells in the skin, blood vessels, limb bud, bronchus, proventriculus, and cardiopleural cavities) had intense TSH staining but little, if any, Pit-1 immunoreactivity. The expression of the TSH gene in these tissues would thus appear to be Pit-1 independent. These results demonstrate the presence of Pit-1 in pituitary and extrapituitary tissues of the domes tic fowl and suggest the involvement of Pit-1 in the extrapituitary expression of TSH in chick embryos may be tissue-specific.
促甲状腺激素（TSH）基因在垂体中的表达被认为依赖于垂体特异性转录因子Pit-1。然而，TSH免疫反应性在外垂体组织中广泛存在，因此，在垂体发生分化之前，研究了胚胎小鸡中这种情况是否可能反映Pit-1的广泛分布。在21天孵化期的头三个月末，小鸡胚胎中的TSH免疫反应性存在于发育中的大脑中的离散细胞中（特别是在围绕第三脑室和中脑导水管的室管膜细胞以及围绕耳泡的细胞中）、脊髓（室管膜细胞）、肝脏（肝细胞）、肺（支气管内衬）、肠道（腺胃内衬）和肢芽（皮肤、肌肉、骨骼和神经纤维中）。在其中一些组织中（特别是在大脑和脊髓室管膜细胞、耳泡细胞和肝脏肝细胞中），TSH免疫反应性的分布与免疫反应性Pit-1的分布重叠，表明Pit-1参与了这些部位的TSH表达。然而，在其他组织中（例如头部的三叉神经和脊髓的边缘套层），Pit-1免疫反应性很强，但TSH免疫反应性很微弱。相反，其他组织（例如皮肤、血管、肢芽、支气管、腺胃和心肺腔中的细胞）有强烈的TSH染色，但几乎没有（如果有的话）Pit-1免疫反应性。因此，这些组织中TSH基因的表达似乎不依赖于Pit-1。这些结果证明了家鸡垂体和外垂体组织中存在Pit-1，并表明Pit-1参与小鸡胚胎中外垂体TSH的表达可能具有组织特异性。
