Prolactin gene expression dynamics and mammotrope function

描述(申请人提供)：催乳素(PRL)由垂体前叶释放，对多种组织的正常功能非常重要，尤其是生殖系统的组织。PRL的表达具有时间特征，暗示着高度的调控。这在很大程度上可以归因于作用于巨噬细胞群体的下丘脑因子的数量和类型，以调节其合成和释放。然而，在理解催乳素调节过程中，一个同样重要的考虑因素是这些因素作用于巨噬细胞的功能状态。我们对单个活体哺乳动物PRL基因表达(PRL-GE)的测量表明，PRL-GE基础水平较低的细胞比基础水平较高的细胞对促甲状腺激素释放激素更敏感，这表明靶细胞的状态对其反应有很大影响。此外，最近的实验表明，这些基础水平的PRL-GE不是恒定的，而是以重复的脉冲或脉冲振荡。这些振荡反映了基础活动的时间变化，这可能决定了细胞对分泌素做出反应的准备情况。最后，这些PRL-GE脉冲被发现依赖于PRL启动子中被称为E-box的特定位置，该E-box与与昼夜基因调节相关的转录因子结合，这表明脉冲的形成是一个高度调控和特定时间的细胞过程。综上所述，很明显，对PRL-GE脉冲的理解对于充分理解PRL的调节及其对生殖系统的影响至关重要。在这项研究中，我们建议检验这样一种假设：“PRL-GE脉冲是控制基础和刺激促乳房功能的基础，因此是正常生殖功能的一个重要方面”。这将通过解决三个具体目标来实现：i)确定单个细胞中PRL-GE和分泌的基本脉冲模式是固定的还是随着生殖状态的变化而变化，ii)阐明单个哺乳动物中PRL-GE脉冲和下丘脑促分泌作用(即刺激或抑制)之间的关系，以及iii)确定在哺乳动物中脉动性PRL-GE背后的分子过程。从这些研究中获得的信息将为了解PRL表达的这一基本方面的作用提供重要的见解，并将显著有助于我们理解影响生殖的高或低催乳素血症的治疗。

DESCRIPTION (provided by applicant): Prolactin (PRL) is released by the anterior pituitary and is important for the proper functioning of a wide variety of tissues, especially those of the reproductive system. PRL is expressed with temporal characteristics that suggest a high degree of regulation. Much of this can be attributed to the number and type of hypothalamic factors that act on the mammotrope population to modulate its synthesis and release. However, an equally important consideration in understanding the process of PRL regulation is the functional state of the mammotropes on which these factors act. Our measurement of PRL gene expression (PRL-GE) in individual living mammotropes revealed that cells with lower basal levels of PRL-GE were more responsive to thyrotropin releasing hormone than cells with higher levels indicating that the state of a target cell greatly impacts its response. Moreover, recent experiments revealed that these basal levels of PRL-GE are not constant, but oscillate in repetitive bursts or pulses. These oscillations reflect temporal changes in basal activity that would likely dictate the readiness of the cell to respond to secretagogues. Finally, these PRL-GE pulses were found to depend on a specific site in the PRL promoter termed an E-box that bind transcription factors associated with circadian gene regulation suggesting that elaboration of a pulse is a highly regulated and specifically timed cellular process. Taken together, it is clear that an understanding of PRL-GE pulses is critical to fully comprehend the regulation of PRL and its impact on the reproductive system. In this study, we propose to test the hypothesis that "pulses of PRL-GE are fundamental to the control of both basal and stimulated mammotrope function and consequently are an important facet of normal reproductive function". This will be accomplished by addressing three SPECIFIC AIMS: I) to determine whether basal pulse patterns of PRL-GE and secretion in individual cells are fixed or change with varying reproductive state, II) to elucidate the relationship between pulses of PRL-GE and hypothalamic secretagogue action (i.e., stimulatory or inhibitory) in single mammotropes, and III) to identify the molecular processes that underlie pulsatile PRL- GE in mammotropes. Information gained from these studies will provide important insight into the role of this fundamental aspect of PRL expression and should contribute markedly to our understanding of the treatment of hyper or hypoprolactinemic conditions that impact reproduction.