Regulation of the melanocyte lineage by the AP2 transcription factor family

描述（由申请人提供）：转录因子是控制所有类型前体细胞和干细胞分化的调控网络中的核心参与者。转录因子调节基因表达是众所周知的，但它们如何调节分化尚不清楚。例如，在某些情况下，给定的转录因子在一种情况下促进细胞分化，而在另一种情况下阻止细胞分化。黑素细胞是探索细胞发育事件的理想模型细胞类型，因为它们的分化很容易评分，它们不是生命所必需的，并且哺乳动物中黑素细胞干细胞的损失很容易通过随后的毛发变灰而明显。此外，编码转录因子和其他调节分子的基因突变引起色素沉着的发育障碍（例如，先天性巨结肠、Tietz综合征、Waardenburg综合征I-IV型、斑驳病）。我们的长期目标是了解黑素细胞谱系发育事件的调控网络。在这里，我们专注于转录因子激活蛋白2家族（TFAP 2A-E）。TFAP 2A似乎阻止黑素细胞干细胞的分化，因为TFAP 2A中的显性突变导致Branchio Oculo Facial Syndrome（BOFS），其特征是过早的头发变白。相比之下，TFAP 2A和它的副产物TFAP 2 E似乎促进胚胎黑素细胞的分化，如我们在斑马鱼中的工作所示。我们假设，在黑素细胞前体，TFAP 2蛋白功能冗余，并与小眼相关转录因子（MITF），黑素细胞生物学的中央调节器，激活基因，影响黑素细胞分化。为了测试该模型，我们将在斑马鱼中进行敲低/加回研究，在小鼠中产生适当的组织特异性双突变体，并对在人黑素细胞中培养的由TFAP 2蛋白和MITF相互激活的基因的启动子进行功能分析。接下来，我们将研究TFAP 2A如何维持黑素细胞干细胞（MSC）的功能。我们假设，在这种情况下，TFAP 2A的关键功能是激活KIT。为了测试这一概念，我们将再次使用斑马鱼进行上位性测试，检查TFAP 2A神经嵴特异性缺失小鼠的毛发变灰，并评估与BOFS中毛发变灰相关的TFAP 2A变体的功能特性。最后，我们将对黑素细胞中TFAP 2A表达的潜在调节因子进行系统分析，并对黑素细胞中TFAP 2A转录靶点进行全面分析，这些将共同将TFAP 2A定位到黑素细胞中的调节网络中。我们的研究将揭示新的遗传和分子网络，黑素细胞的正常和病理发展的基础。从这项工作中产生的新知识将是有价值的，特别是在Waardenburg综合征和BOFS的病因。更一般地说，它将阐明在一个易处理的模型细胞类型的分化的转录调控。

DESCRIPTION (provided by applicant): Transcription factors are central players in the regulatory networks that control differentiation in all types of precursor cells and stem cells. Itis well known that transcription factors regulate gene expression, but it is unclear how they regulate differentiation. For instance, in some cases a given transcription factor promotes cell differentiation in one context, and prevents it in another. Melanocytes are an ideal model cell type to explore cellular developmental events because their differentiation is easily scored, they are not essential for life, and loss of melanocyte stem cells in mammals is readily apparent by the consequent hair graying. Moreover, mutations in genes encoding transcription factors and other regulatory molecules cause developmental disorders of pigmentation (e.g., Hirschsprung's disease, Tietz syndrome, Waardenburg syndrome types I- IV, piebaldism). Our long-term objective is to understand the regulatory network governing developmental events in the melanocyte lineage. Here we focus on the transcription factor Activator Protein 2 family (TFAP2A-E). TFAP2A appears to prevent differentiation of melanocyte stem cells, because dominant mutations in TFAP2A cause Branchio Oculo Facial Syndrome (BOFS), which features premature hair graying. By contrast, TFAP2A and its paralog TFAP2E appear to promote differentiation of embryonic melanocytes, as shown by our work in zebrafish. We hypothesize that within melanocyte precursors, TFAP2 proteins function redundantly, and in parallel with microphthalmia-associated transcription factor (MITF), a central regulator of melanocyte biology, to activate genes that effect melanocyte differentiation. To test this model we will conduct knock-down/add-back studies in zebrafish, generate appropriate tissue- specific double mutants in mice, and conduct functional analysis of the promoter of a gene mutually activated by TFAP2 proteins and MITF in cultured in human melanocytes. Next we will examine how TFAP2A functions to maintain melanocyte stem cells (MSC). We hypothesize that in this context, the key function of TFAP2A is to activate KIT. To test this notion we will use zebrafish again for epistasis tests, examine hair graying in a mouse with neural-crest-specific deletion of TFAP2A, and assess functional properties of TFAP2A variants associated with hair graying in BOFS. Finally, we will conduct systematic analyses of potential regulators of TFAP2A expression in melanocytes, and a global analysis of TFAP2A transcriptional targets in melanocytes, which together will position TFAP2A into a regulatory network in melanocytes. Our studies will shed light on novel genetic and molecular networks that underlie normal and pathological development of melanocytes. The new knowledge generated from this work will be of value specifically in the etiology of Waardenburg syndrome and BOFS. More generally, it will illuminate the transcriptional regulation of differentiation in a tractable model cell type.