Specification and Molecular Control of the Hair Follicle Inductive Mesenchyme

项目摘要 毛囊（HF）是一个很好的模型系统，用于研究分子之间的串扰， 干/祖细胞和微环境或生态位。在胚胎HF形成过程中， 毛基板中的祖细胞接收来自真皮冷凝物（DC）的生态位信号，真皮冷凝物是成熟HF的前体 间充质，即真皮乳头（DP）和真皮鞘（DS）。DP细胞则作为毛球的小生境 祖细胞协调连续的毛发生长和隆突/生殖干细胞启动新的毛发周期。的 DS在毛发生长过程中的作用尚不清楚。在毛发周期中，最近发现了DS细胞的一个亚群 当受到以下因素的挑战时， 反复脱毛引起的毛发循环。重要的是，分离的成熟DP细胞可以诱导新的HF形成 移植后，提示DS也有潜力，但移植物中不完全的细胞示踪排除了 明确的解释。有几个关键的问题仍然没有答案：什么是发展谱系 胚胎DC与成熟DS和DP的关系？什么是确定的高频感应能力， DS？对于HF的初始生长，DS的基本功能是什么？什么样的分子机制 控制DS功能？通过使用广泛的转录组知识和遗传工具，我们最近 为胚胎DC和DP开发的，我们现在已经建立了新的初步数据的条件， 回答这些问题，并严格测试的假设，DS构成了一个独特的 间充质HF小生境。有了三个专门的目标，我们将确定增殖和克隆动力学 通过在整个形态发生过程中进行脉冲追踪标记保留实验， 使用已建立的诱导型Cre驱动因子和报告小鼠标记单个DC细胞。这些研究将提供一个 严格评估DS和DP的不同增殖倾向和谱系关系。我们 然后将首次使用转基因荧光报告基因同时分离纯DS细胞和DP 小鼠，系统地定义独特的DS分子特征，并使用定义和可追溯的细胞移植 条件，以明确地确定其在已建立的体内试验中的毛发诱导潜力。最后我们将 研究鉴定的DS转录因子Satb 2和其他新的DS特征的功能作用 通过用我们建立的诱导型Cre系进行体内基因消融来检测基因。这些研究的结果将 揭示了DS和DP生态位的动态和功能关系，明确了DS的容量 作为毛发诱导间充质，并实现了DS基因调控的第一个分子见解。最终 这项工作的目的是扩大我们的知识，干细胞调控的利基，这在HF的背景下， 对于开发再生疗法以完全恢复功能性皮肤（包括HFs， 由于我们对DP和DS调节和功能的了解有限，目前缺乏这种技术。

Project Summary The hair follicle (HF) is an excellent model system for studying the molecular cross-talk between stem/progenitor cells and the microenvironment or niche. During embryonic HF formation epidermal progenitors in hair placodes receive niche signals from dermal condensates (DC), precursors of the mature HF mesenchyme, i.e. the dermal papilla (DP) and dermal sheath (DS). DP cells then act as niche for hair bulb progenitors to coordinate continuous hair growth and for bulge/germ stem cells to launch a new hair cycle. The role of the DS during hair growth is unclear. During the hair cycle, a subset of DS cells was recently identified that replenishes the DS and to some extent could contribute to the DP compartment when challenged by repeated depilation-induced hair cycling. Importantly, isolated mature DP cells can induce new HF formation after transplantation, a potential suggested for the DS as well, but incomplete cell tracing in grafts precluded definitive interpretation. Several key questions remain unanswered: What is the developmental lineage relationship between embryonic DC and mature DS and DP? What is the definitive HF induction capacity of DS? What are essential functions of the DS for initial HF growth? What are the molecular mechanisms that control DS functions? By employing the extensive transcriptome-knowledge and genetic tools we recently developed for embryonic DC and DP, we have now established with new preliminary data the conditions to answer these questions and rigorously test the hypothesis that the DS constitutes a distinct mesenchymal HF niche. With three dedicated Aims, we will determine the proliferative and clonal dynamics with pulse-chase label retention experiments throughout morphogenesis and by lineage tracing of selectively labeled single DC cells using established inducible Cre drivers and reporter mice. These studies will provide a rigorous assessment of the differential proliferative proclivity and lineage relationship of the DS and DP. We will then isolate for the first time simultaneously pure DS cells and DP using transgenic fluorescent reporter mice, systematically define the unique DS molecular signature and use defined and traceable cell grafting conditions to unequivocally determine their hair-inducing potential in established in vivo assays. Finally, we will investigate the functional role of the identified DS transcription factor Satb2 and other novel DS signature genes by in vivo gene ablation with our established inducible Cre lines. The results from these studies will reveal the dynamics and functional relationship of DS and DP niches, definitively determine the capacity of DS as hair-inductive mesenchyme, and achieve the first molecular insights into DS gene regulation. The ultimate goal of this work is to expand our knowledge of stem cell regulation by the niche, which in the context of the HF will be paramount for developing regenerative therapies to fully restore functional skin including HFs, a technology which currently is lacking due to our limited understanding of DP and DS regulation and function.