Understanding how the master transcriptional regulator HOXA5 defines cell fate in the developing embryo

细胞类型特异性转录程序的适当控制对于正常发育至关重要。单个转录调节因子的突变通常产生具有器官特异性后果的多效性表型。因此，理解单个转录因子如何通过控制特定的转录程序来赋予细胞和组织其身份是至关重要的。HOX蛋白是进化上保守的转录因子，在胚胎发生、器官发生和组织稳态中起关键作用。它们的突变导致多种和各种发育缺陷和疾病。尽管它们在许多细胞类型中广泛表达，但HOX蛋白以上下文依赖的方式执行其调节功能。它们与类似的TNAT基序丰富的DNA结合位点结合，但在体内赋予不同的调节作用，从而提出了HOX转录产物的特异性如何实现的根本问题。虽然Hox基因的发育作用已经确定，但了解它们如何发挥作用仍有待于靶基因的鉴定。因此，HOX蛋白代表了确定单个转录因子如何支配细胞命运的理想候选物。我们的长期目标是确定HOX转录因子如何在哺乳动物发育过程中以高度上下文依赖的方式调节靶基因表达。我们使用HOXA 5作为模型，因为小鼠中Hoxa 5基因功能的丧失导致过多的良好表征的表型，最重要的是，由于呼吸系统畸形的组合，导致出生时死亡。这些缺陷包括由软骨异常引起的气管闭塞，由于分支减少、发育不全和异常细胞分化引起的肺形态异常，以及改变的膈肌神经支配和肌肉组织。这些表型引起严重的人类疾病，如气管狭窄，肺发育不全和隔膜隆起。没有其他单一的Hox突变体呈现这样一个明显的呼吸系统表型，揭示了Hoxa5在这个发育过程中的功能优势。Hoxa5在呼吸系统中的多效性作用表明细胞特异性机制，并使Hoxa5成为研究单个HOX蛋白如何实现细胞特异性以协调器官系统发育的理想模型。我们假设HOXA 5转录因子通过激活常见的转录程序发挥其部分功能，但也通过调节不同的，上下文特异性效应子。我们的目标是确定参与HOXA 5行动的分子机制，在呼吸系统的形成，以阐明HOXA 5如何获得功能细胞特异性。我们的目标是：1.鉴定和比较HOXA 5主调节因子在发育中的气管、肺和膈肌中控制的基因网络2.确定HOXA 5在气管形成的特定背景下功能的遗传和细胞机制

Proper control of cell-type specific transcriptional programs is critical for normal development. Mutation of a single transcriptional regulator often produces pleiotropic phenotypes with organ-specific consequences. Therefore, it is fundamental to understand how a single transcription factor confers to cells and tissues their identity by controlling specific transcriptional programs. HOX proteins are evolutionary conserved transcription factors that play critical roles in embryogenesis, organogenesis and tissue homeostasis during postnatal life. Their mutations lead to multiple and various developmental defects and diseases. Despite their broad expression in numerous cell types, HOX proteins perform their regulatory functions in a context-dependent fashion. They bind to similar TNAT motif-rich DNA-binding sites, but confer different regulatory actions in vivo, raising the fundamental question of how specificity of HOX transcriptional outputs is attained. While the developmental role of Hox genes is established, understanding how they act still awaits the identification of target genes. Thus, HOX proteins represent ideal candidates to determine how individual transcription factors govern cell fate. Our long-term objective is to define how HOX transcription factors regulate target gene expression in a highly context-dependent manner during mammalian development. We use HOXA5 as a model, because the loss of Hoxa5 gene function in mice results in a plethora of well-characterized phenotypes and, most importantly, in death at birth due to the combination of respiratory system malformations. These defects include trachea occlusion resulting from cartilage anomalies, lung dysmorphogenesis due to reduced branching, hypoplasia and abnormal cell differentiation, and altered diaphragm innervation and musculature. These phenotypes evoke severe human diseases such as tracheal stenosis, lung hypoplasia and diaphragm eventration. No other single Hox mutants present such an overt respiratory system phenotype revealing the functional predominance of Hoxa5 in this developmental process. Hoxa5 pleiotropic action in the respiratory system suggests cell-specific mechanisms, and makes Hoxa5 an ideal model for studying how individual HOX proteins achieve cell-specificity to orchestrate organ system development. We hypothesize that HOXA5 transcription factor exerts part of its functions through activation of common transcriptional programs but also via the regulation of distinct, context-specific effectors. Our objectives are to define the molecular mechanisms involved in HOXA5 action during the formation of the respiratory system in order to elucidate how HOXA5 attains functional cell-specificity. Our aims are to: 1.Identify and compare the gene networks controlled by the HOXA5 master regulator in the developing trachea, lung and diaphragm 2.Determine the genetic and cellular mechanisms of HOXA5 function in the specific context of trachea formation