Pituitary thyrotropes are specialized cells that produce thyroid stimulating hormone, a critical factor for growth and maintenance of metabolism. The transcription factors POU1F1 and GATA2 have been implicated in thyrotrope fate and regulation of Tshb transcription, but no transcriptomic or epigenetic analyses of these cells has been undertaken. The goal of this work was to discover key elements that drive thyrotrope fate. We identified the transcription factors and epigenetic changes in chromatin that are associated with differentiation of POU1F1-expressing progenitors into thyrotropes using cell lines that represent an early, undifferentiated Pou1f1 lineage progenitor (GHF-T1) or a committed thyrotrope (TαT1). We generated and integrated genome-wide information about DNA accessibility, histone modification, POU1F1 transcription factor binding and RNA expression data to identify regulatory elements and candidate transcriptional regulators. We identified POU1F1 binding sites that were unique to each cell line. POU1F1 binding sites are commonly associated with bZIP transcription factor consensus binding sites in GHF-T1 cells and HLH (Helix-Turn-Helix) or basic Helix-Turn-Helix (bHLH) factors in TαT1 cells, suggesting that some classes of transcription factors may recruit or cooperate with POU1F1 binding to unique sites. We validated enhancer function of novel elements we mapped near Cga, Pitx1, Gata2, and Tshb by transfection in TαT1 cells. Finally, we confirmed that an enhancer element near Tshb can drive expression in thyrotropes of transgenic mice, and we demonstrate that GATA2 enhances Tshb expression through this element. These data extend the ENCODE analysis to an organ that is critical for growth and metabolism. This information may be valuable for understanding pituitary development and disease pathogenesis.

中文翻译：

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垂体促甲状腺素签名基因和调控元件的鉴定

垂体促甲状腺激素是产生甲状腺刺激激素的专门细胞，甲状腺刺激激素是生长和维持新陈代谢的关键因素。转录因子POU1F1和GATA2与甲状腺素命运和Tshb转录的调控有关，但尚未对这些细胞进行转录组或表观遗传学分析。这项工作的目的是发现驱动甲状腺激素命运的关键因素。我们使用代表早期，未分化的Pou1f1的细胞系，鉴定了与表达POU1F1的祖细胞分化为促甲状腺激素相关的染色质的转录因子和表观遗传学变化。血统祖细胞（GHF-T1）或定型甲状腺素（TαT1）。我们生成并整合了有关DNA可及性，组蛋白修饰，POU1F1转录因子结合和RNA表达数据的全基因组信息，以识别调控元件和候选转录调控因子。我们确定了每个细胞系唯一的POU1F1结合位点。POU1F1结合位点通常与GHF-T1细胞中的bZIP转录因子共有结合位点以及TαT1细胞中的HLH（Helix-Turn-Helix）或基本Helix-Turn-Helix（bHLH）因子相关，这表明某些类别的转录因子可能与招募或与绑定到唯一网站的POU1F1合作。我们验证了我们映射到Cga，Pitx1，Gata2和附近的新元素的增强子功能。通过在TαT1细胞中转染Tshb。最后，我们证实了Tshb附近的增强子元件可以驱动转基因小鼠的促甲状腺素中的表达，并且我们证明GATA2通过该元件增强Tshb的表达。这些数据将ENCODE分析扩展到对生长和代谢至关重要的器官。该信息对于了解垂体发育和疾病发病机理可能是有价值的。