Making a head: connecting reciprocal signaling to cell reprogramming

脊椎动物头部具有惊人的能力来适应栖息地和生态位的功能要求。这其中的中心是脑神经脊细胞(Cnc)，它是头部最可变的结构：面部骨骼、软骨和牙齿的关键贡献者。少数进化保守、反复使用的细胞外信号通路控制着大多数面部结构的发育。同样的途径也是导致脸型变化的主要因素。这是如何实现的？在这个研究项目中，我们将研究骨形态发生蛋白(BMPs)是如何控制CNCs的分化的，BMPs是一个进化保守的分泌型信号分子家族，以及细胞内表观遗传重新编程(以ANKRD11为代表)如何允许在整个发育过程中重复使用这些BMPs。我们专注于对数控技术有重大贡献的结构，下颌骨和颅底的牙齿和软骨。话题1：牙齿矿化。牙齿是研究上皮-间充质串扰的极佳模型，涉及形成釉质的成釉细胞(口腔上皮)和形成牙本质的成牙本质细胞(cnc来源的间充质)。虽然牙齿硬组织的形成非常牢固，但它同时也很灵活，允许广泛的牙齿多样性和功能。在这里，我们将研究ANKRD11如何编程分泌矿物质的成牙本质细胞和成釉细胞，以及Bmp6/BMP7如何控制牙齿矿化的启动时间。主题2：Meckel‘s软骨的生长和成熟。下颌骨围绕着一个暂时性的胚胎软骨形成，称为梅克尔氏软骨(MC)。MC控制下颌的形状和大小。Bmp7和Ankrd11的缺失都会导致下颌骨发育迟缓。使用体内和体外方法，我们将研究MC分化的顺序步骤，通过计算机控制或软骨特异性缺失这些基因，以揭示这一关键胚胎结构生长和成熟的详细分子调控。话题3：颅底的骨生长。形成颅骨下部不可见部分的颅底(CB)是头部形状变化的主要因素。CB由软骨模板形成，软骨模板通过一种称为软骨内骨化的过程骨化。BMP2、BMP7和Ankrd11的缺失都会影响CB的生长和成骨。在这里，我们将通过对NC或软骨特异性缺失BMP2、Bmp7和Ankrd11的胚胎的表型比较研究，探讨细胞外信号和细胞内表观遗传重编程如何控制软骨内成骨的过程。意义和影响：使用三个定义明确的颅面结构并行研究细胞外信号和细胞内重编程将提供独特的见解，了解在这些面部结构的发育过程中细胞命运决定是如何控制和维护的。这些见解将有助于理解颅面发育强大而可塑性的本质。

The vertebrate head has an amazing capacity to adapt to functional requirements of habitats and ecological niches. Central to this are cranial neural crest cells (CNC), which are key contributors to the most variable structures of the head: the facial bones, cartilages, and teeth. A handful of evolutionary conserved, reiteratively used, extracellular signaling pathways control development of most facial structures. The same pathways are also major contributors to facial shape variation. How is this achieved? In this research program, we will investigate how differentiation of CNCs is controlled by Bone Morphogenetic Proteins (BMPs), a family of evolutionary conserved, secreted signaling molecules, and how intracellular epigenetic reprogramming (represented by ANKRD11) allows the reiterated use of these BMPs throughout development. We focus on structures with major CNC contribution, teeth and cartilages of the mandible and cranial base. Topic 1:  Tooth mineralization. Teeth are an excellent model to study epithelial-mesenchymal crosstalk involving enamel-forming ameloblasts (oral epithelium) and dentin-forming odontoblasts (CNC-derived mesenchyme). While dental hard tissue formation is remarkably robust, it is at the same time flexible, allowing for wide dental diversity and functionality. Here, we will investigate how ANKRD11 programs mineral-secreting odonto- and ameloblasts and how timing of initiation of tooth mineralization is controlled by BMP6/BMP7. Topic 2: Growth and maturation of Meckel's cartilage. The lower jaw (mandible) forms around a transient embryonic cartilage termed Meckel's cartilage (MC). MC controls mandible shape and size. Loss of Bmp7 and Ankrd11 both lead to stunted growth of the mandible. Using in vivo and in vitro approaches, we will investigate the sequential steps of MC differentiation using CNC- or cartilage-specific deletion of these genes to unravel the detailed molecular regulation of growth and maturation of this critical embryonic structure. Topic 3:Bone growth at the cranial base. The cranial base (CB) forming the lower, invisible part of the skull is a major contributor to head shape variation. The CB forms from cartilage templates that ossify through a process called endochondral ossification. Loss of Bmp2, Bmp7 and Ankrd11 all affect CB growth and ossification. Here, we will investigate how extracellular signals and cell-intrinsic epigenetic reprogramming control the process of endochondral ossification through comparative phenotypic studies on embryos with NC- or cartilage-specific deletion of Bmp2, Bmp7, and Ankrd11. Significance and impact: The investigation of extracellular signaling and intracellular reprogramming in parallel using three well-defined craniofacial structures will offer unique insight into how cell fate decisions are controlled and enshrined during development of these facial structures. These insights will help understanding the robust yet plastic nature of craniofacial development.