TSHR and thyrocyte development

我们的长期目标是阐明甲状腺干细胞分化为定型甲状腺细胞的分子机制。我们特别关注促甲状腺激素（TSH），因为它是控制甲状腺生长和功能的主要激素。为了研究TSH是否直接调节甲状腺发育，我们通过用绿色荧光蛋白替换mTSHR基因的外显子1来产生TSHR无效小鼠。我们发现TSHR小鼠严重甲状腺功能减退，并在4周时死亡。杂合子小鼠不受影响。在TSHR +/ -和TSHR-/-小鼠的甲状腺滤泡中检测到强烈的绿色荧光。值得注意的是，TSHR-/-小鼠的卵泡发育不良，卵泡细胞较少，这意味着卵泡的生长和分化依赖于TSH。为了进入发育的早期胚胎阶段，我们获得了TSHR +/ - ES细胞系。除了提供 通过对体内甲状腺中TSHR的功能表征，这些ES细胞使我们能够在ES细胞分化模型中追踪甲状腺细胞诱导及其向甲状腺细胞谱系的特化。提出了两个具体目标。具体目标1将集中于ES细胞分化过程中甲状腺谱系的诱导和特化。我们将研究TSHR和TSH在TSHR +/ -和TSHR -/- ES细胞体外分化过程中何时表达。我们还将研究TSHR +/-和TSHR -/- ES细胞中TSHR相对于指示甲状腺谱系的分化标志物的时间和空间表达。更重要的是，我们将描述甲状腺细胞发育中的TSH/TSHR信号传导，并研究胰岛素和胰岛素生长因子-1是否可以上调甲状腺球蛋白，这是成熟甲状腺细胞的一个特征。具体目标2将使用实际小鼠胚胎或ES细胞分化模型研究TSH阳性群体的体内甲状腺细胞潜能。首先，我们将进一步表征TSHR +/ -和TSHR -/-小鼠胚胎在植入后发育过程中的甲状腺表型。我们接下来将研究来自胚胎的TSHR阳性细胞是否 组织具有甲状腺细胞潜能。最后，我们将确定来自ES细胞的TSHR阳性细胞是否可以在SCID小鼠中分化为功能性甲状腺细胞。这些实验的结果将提供一个更清楚的了解胚胎甲状腺细胞的特点，以及这些细胞如何与确定的甲状腺细胞谱系。这些研究可能不仅对我们理解正常甲状腺发育具有重要意义，而且可能为人类疾病的潜在机制提供见解。

Our long-term goal is to elucidate the molecular mechanisms by which thyroid stem cells differentiate into definitive thyrocytes. We specifically focus on thyroid stimulating hormone (TSH), as it is the major hormone in the control of thyroid growth and function. To examine whether TSH directly regulates thyroid development, we generated a TSHR null mouse by replacing exon 1 of the mTSHR gene with green fluorescent protein. We found that TSHR''' mice were severely hypothyroid and died at 4 weeks. Heterozygous mice were unaffected. Intense green fluorescence was detected in thyroid follicles of both TSHR +/ - and TSHR-/- mice. Of note is that follicles in TSHR-/- mice were poorly developed with fewer follicular cells, implying that the follicular growth and differentiation were dependent on TSH. To access early embryonic stages of development, we obtained the TSHR +/ - ES cell line. In addition to providing functional characterization of the TSHR in the thyroid in vivo, these ES cells have enabled us to track thyrocyte induction and its specification to the thyroid cell lineage in the ES cell differentiation model. Two specific aims are proposed. Specific aim 1 will focus on the induction and specification of thyroid lineage during ES cell differentiation. We will investigate when are TSHR and TSH expressed during in vitro differentiation of TSHR +/ - and TSHR -/- ES cells. We will also examine the temporal and spatial expression of TSHR relative to differentiation markers indicative of thyroid lineages in TSHR +/- and TSHR -/- ES cells. More importantly, we will characterize TSH/TSHR signaling in thyrocyte development and investigate whether insulin and insulin growth factor-1 can up-regulate thyroglobulin, a characteristic of mature thyrocytes. Specific Aim 2 will investigate the in vivo thyrocyte potential of TSHR-positive populations using actual murine embryos or ES cell differentiation model. First, we will further characterize the thyroid phenotypes of TSHR +/ - and TSHR -/- mouse embryos during postimplantation development. We will next investigate whether TSHR-positive cells from embryonic tissues have thyrocyte potential. Finally, we will determine whether TSHR-positive cells from ES cells can differentiate into functional thyrocytes in SCID mice. The outcome of these experiments will provide a clearer understanding of the characteristic of embryonic thyroid cells and of how these cells relate to definitive thyrocyte lineage. These studies may have important implications not only for our understanding of normal thyroid development but may provide insights into mechanisms underlying human diseases.