Cell differentiation and secretory products of hypophyseal pars tuberalis

围绕正中隆起和漏斗柄的垂体部由特定的分泌细胞和支持细胞或滤泡细胞组成。结节(PT)特异性细胞表达糖蛋白激素的α亚单位，表达α亚单位的mRNA。在鸡胚中，α亚单位的基因和蛋白在胚胎3.5d开始出现在Rathke囊中。E6时，黄体生成素免疫反应阳性的促性腺激素细胞首先出现在远侧部。E8时，位于正中隆起附近的结节原始部在PAR远端外侧顶端形成。原基表达α亚单位基因和蛋白的强信号。因此，远侧部和结节部的原基都表达α亚单位。该亚基可能在腺垂体的细胞分化过程中发挥作用。此外，结节α亚单位基因的表达水平也随光周期的变化而变化。连续光照30天后，PT特异性细胞内充满较大的分泌颗粒，表现为分泌活性降低，结节α亚单位基因表达水平明显降低。而连续黑暗暴露30天的雏鸡，PT特异性细胞胞浆和胞核面积增大，分泌颗粒的胞吐特征更为明显。在持续黑暗条件下，α-亚基基因表达水平升高。这些数据表明，PT特异性细胞对光周期变化有反应。松果体切除后，结节部α亚单位基因表达水平升高。然而，在松果体摘除后的连续光照或黑暗条件下，鸡的结节部细胞活性和α亚单位基因水平的变化与未手术动物相似。

The hypophyseal pars tuberalis surrounding the median eminence and infundibular stalk is composed of specific secretory cells and sustentacular or follicular cells. The pars tuberalis (PT)-specific cells are immunoreactive for α-subunit of glycoprotein hormones and express α-subunit mRNA.In chick embryos, the α-subunit mRNA and protein began to appear in the Rathke's pouch at embryonic day (E) 3.5. At E6, gonadotrophs immunoreactive for LH were first detected in the pars distalis. At E8, the pars tuberalis primordium located close to the median eminence was formed at the lateral apical end of the par distalis. The primordium expressed intense signal for α-subunit mRNA and protein. Thus, both primordia of the pars distalis and pars tuberalis expressed α-subunit. This subunit may play a role in the cytodifferentiation of the adenohypophyses. In addition, α-subunit mRNA level in the pars tuberalis was changed depending on photoperiods. In chicks exposed to continuous light for 30 days, the PT-specific cells were filled with enlarged secretory granules, showing the reduction of secretory activity and α-subunit mRNA level in the pars tuberalis markedly decreased. On the other hand, in chicks exposed to continuous darkness for 30 days, the PT-specific cells displayed enlarged cytoplasmic and nuclear areas and exocytotic features of secretory granules were more frequent. Alpha-subunit mRNA level was increased under continuous darkness. These data indicate that the PT-specific cells are responsive to photoperiodic changes. After pinealectomy, α-subunit mRNA level in the pars tuberalis was increased. However, in chicks under continuous light or darkness after pinealectomy, the cell activity and α-subunit mRNA level in the pars tuberalis were similar in changes to those of unoperated animals.