Photoperiodic regulation of prolactin gene expression in the syrian hamster by a pars tuberalis-derived factor
Photoperiodic regulation of prolactin gene expression in the syrian hamster by a pars tuberalis-derived factor
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DOI：
10.1046/j.1365-2826.2001.00611.x
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发表时间：
2001-02-01
影响因子：
3.2
通讯作者：
Loudon, ASI
中科院分区：
文献类型：
--
作者：
Stirland, JA;Johnston, JD;Loudon, ASI
叙利亚仓鼠在催乳素分泌方面表现出明显的季节性变化。本研究的目的是分析催乳素基因表达的光周期调节的性质，并确定褪黑激素和垂体前叶结节部在这一过程中的作用。长日照（16小时：8小时，光照：黑暗）的仓鼠与短日照（8小时：16小时，光照：黑暗）8-12周的仓鼠相比，垂体泌乳素基因表达增加，仅限于远部。单细胞原位杂交分析表明，光周期对远端部细胞表达催乳素mRNA的比例没有影响，但改变了每个细胞表达催乳素mRNA的频率分布，因此在较长的光周期中，更大比例的细胞被招募到高表达的群体中。在体外共培养的仓鼠结核部分片段中，稳定转染的GH(3)细胞中催乳素启动子驱动的荧光素酶活性以剂量和持续时间依赖的方式增加。来自仓鼠和羊结节部的条件培养基也激活了催乳素启动子。此外，基底和福斯克林刺激的条件培养基增加了远部细胞原代培养中催乳素mRNA的表达。褪黑素降低了结核部条件培养基的活性，但对远部细胞培养中催乳素mRNA的表达和分泌没有直接影响。最后，来自长光周期仓鼠的结节部片段比来自短光周期仓鼠的片段更能刺激催乳素基因启动子活性。总之，本研究首次在季节性哺乳动物中提供证据，证明催乳素的合成依赖于结核源性因子的光周期调节。我们的数据进一步支持了催乳素基因表达的季节性调节取决于结节部对远端乳营养细胞的褪黑激素依赖性旁分泌作用的假设。
Syrian hamsters exhibit a marked seasonal variation in prolactin secretion. The aim of this study was to analyse the nature of the photoperiodic regulation of prolactin gene expression, and to define the role of melatonin and the pars tuberalis of the anterior pituitary in this process. Pituitary prolactin gene expression, restricted to the pars distalis, was increased in hamsters maintained in long daylengths (16 h:8 h, light:dark) compared to hamsters exposed to short daylengths (8 h:16 h, light:dark) for 8-12 weeks. Analysis of single cells by in situ hybridization showed that photoperiod had no effect on the percentage of pars distalis cells expressing prolactin mRNA, but shifted the frequency distribution of prolactin mRNA expression per cell, such that in long photoperiods a greater proportion of cells were recruited to a higher expressing population. In vitro coculture of hamster pars tuberalis fragments increased prolactin promoter-driven luciferase activity in stably transfected GH(3) cells in a dose- and duration-dependent manner. Conditioned medium from hamster and ovine pars tuberalis also activated the prolactin promoter. Furthermore, basal and forskolin-stimulated conditioned medium from hamster pars tuberalis increased prolactin mRNA expression in primary cultures of pars distalis cells. Melatonin attenuated the activity of pars tuberalis-conditioned medium but had no direct effect on either prolactin mRNA expression or secretion in pars distalis cell cultures. Finally, pars tuberalis fragments from long photoperiod hamsters stimulated prolactin gene promoter activity to a greater extent than those from short photoperiod hamsters. in conclusion, this study provides the first evidence in a seasonal mammal that the synthesis of prolactin depends on photoperiodic modulation of a pars tuberalis-derived factor. Our data support further the hypothesis that seasonal modulation of prolactin gene expression depends upon a melatonin-dependent paracrine action of the pars tuberalis on pars distalis lactotrophic cells.