Mechanisms of development of the pituitary progenitors with pit-1 expression into growth hormone and prolactin cells

据信，生长激素（GH）和催乳素（PRL）源自共同的祖先基因，而每种激素都是由哺乳动物脑垂体前叶中不同类型的细胞分泌的。人们也普遍认为，GH和PRL细胞是从共同的前体细胞分化而来的，因为这些细胞类型通常表达垂体特异性转录因子pit-1。然而，负责这两种细胞类型分化的机制仍然不清楚。在本研究中，我试图检查这两种细胞类型是独立地从前体细胞分化还是其中一种先分化并成为另一种细胞类型的母细胞。PCR扩增了报告基因的细胞类型特异性表达所需的GH、PRL和pit-1的5 '上游区域，构建了表达荧光蛋白CFP的报告质粒，在这些推动者的指导下。这些质粒成功地标记GH或PRL细胞与CFP时，从成年雄性大鼠的垂体细胞。然而，CFP的表达是非常低的，当引入到胎儿垂体，可能是由于在胎儿垂体细胞的弱启动子活性。这些结果表明，进一步提高检测系统的灵敏度是必要的，应用该方法的研究中发生在胎儿垂体细胞类型的确定。我还建立了PCR技术检测激素mRNA在单个垂体细胞中的表达。因此，揭示了近50%的GH细胞也表达PRL mRNA，这表明存在出乎意料的大量表达多种mRNA的细胞。因此，研究单个细胞中GH和PRL基因表达的调控机制具有重要意义。

It is believed that growth hormone(GH) and prolactin(PRL) are derived from a common ancestral gene, whereas each hormone is secreted from distinct cell type in the anterior pituitary gland in mammals. It is also widely accepted that GH and PRL cells are differentiate from the common precursor cells since these cell types commonly express pituitary specific transcription factor, pit-1. The mechanisms responsible for the differentiation of these two cell types are, however, still obscure. In this study, I tried to examine whether these two cell types differentiate from precursors independently or one of them differentiate first and become the mother cells of another cell type.The 5'-upstream region of GH, PRL, and pit-1 that required for the cell type specific expression of the reporter gene were PCR amplified and the reporter plasmids were constructed that express the fluolescent protein, CFP, under the direction of these promoters. These plasmids successfully labeled GH or PRL cells with CFP when introduced into isolated pituitary cells from adult male rat. However, the expression of CFP was extremely low when introduced into fetal pituitary gland, probably due to the weak promoter activity in the fetal pituitary cells. These results indicate that further enhancement of the sensitivity of the detection system is required for the application of this method to the study of cell type determination that occurs in the fetal pituitary gland.I also established the PCR-technology for the detection of the hormone mRNA expression in the single pituitary cells. As a consequence, it is revealed that nearly 50% of GH cells also express PRL mRNA, suggesting that there are an unexpectedly large number of cells that express multiple mRNAs. It is considered to be of importance to establish the regulatory mechanisms for the expression of GH and PRL gene in the single cells.