The role of the primitive choana in amniote craniofacial morphogenesis

我建议研究羊膜腔的发育，特别强调确定对胚胎口腔其他关键因素的可能影响，如次级腭的形成。choanae是连接口腔和鼻通道的内鼻孔，对正确的鼻呼吸至关重要。在哺乳动物中，choanae被第二腭覆盖，因此直接通向鼻咽。然而，在大多数其他爬虫类羊膜动物中，choanae直接打开到口腔。尽管它们在所有脊椎动物中都存在，但很少有人关注这种结构。这一点尤其值得注意，因为人类的后鼻孔发育不正确（例如，将后鼻孔与鼻道分开的口鼻膜保留），导致后鼻孔闭锁（CA），可导致婴儿死亡。最近的几项研究已经确定了遗传途径，当受到干扰时，可以在小鼠模型中引起CA。此外，我们的初步研究表明，choanae表达的关键发育基因涉及从牙齿发育的开始到第二腭的生长和融合等颅发育的各个方面。我推测，在非常年轻的胚胎中，choanae离得足够近，足以影响口腔顶部邻近结构的发育。因此，我提出了一系列的研究，这些研究将有助于描述羊膜在有和没有第二腭的情况下与正常后鼻孔发育相关的组织特异性变化。随后，我试图确定分子途径的可能作用，我们已经观察到在choanae中特别活跃。在这些研究中，我将使用两种模式生物，鸡和老鼠，以及一种非模式生物，乌龟。这三个羊膜代表了三种不同类型的次腭。老鼠有完整的次级上颚，鸡有天然的腭裂，乌龟有原始的上颚。这些比较研究将使我们能够比较在choanae周围组织中表达的基因，并确定那些与闭合和打开的上颚相关的基因。接下来，我将培养含有choanae的胚胎腭，并将增加或减少在该区域富集的不同信号分子的水平。我还会植入微型箔状屏障来阻止声波信号到达上颚。这些干预对口鼻膜破裂和腭架形成的影响将被研究。在鸡中，将通过在鸡蛋中向胚胎添加信号或其抑制剂来研究对腭骨的长期影响。这将是第一次对choanae的胚胎发育进行研究。研究人员将研究面部新信号中心的存在，并发现面部异常（如腭裂）的新分子原因。

I propose to study the development of the amniote choana, with specific emphasis on identifying putative influences on other key elements of the embryonic oral cavity such as secondary palate formation. The choanae are the internal nares which connect the oral cavity to the nasal passages and are crucial for proper nasal respiration. In mammals, the choanae are covered by the secondary palate and therefore, open directly into the nasopharynx. In most other reptilian amniotes however, the choanae open directly into the oral cavity. Despite their persistence in all vertebrates, very little focus has been placed on this structure. This is especially remarkable since incorrect development of the choana (e.g. retention of the oronasal membrane separating the choana from the nasal passage) in humans, which results in choanal atresia (CA), can lead to infant mortality. Several recent studies have identified genetic pathways which, when perturbed, can cause CA in mouse models. Additionally, our preliminary studies have shown that choanae express key developmental genes which are implicated in various other aspects of cranial development ranging from the initiation of tooth development to the growth and fusion of the secondary palate. I hypothesize that in very young embryos the choanae are in close enough proximity to influence development of the adjacent structures in the roof of the oral cavity. Therefore, I have proposed a series of studies which will serve to characterize the tissue specific changes associated with proper choanal development in amniotes with and without a secondary palate. Subsequently, I seek to identify the likely roles of the molecular pathways which we have observed to be specifically active in the choanae. For these studies, I will use two model organisms, chicken and mouse, as well as a non-model organism, the turtle. These three amniotes represent three different types of secondary palates. Mice have a complete secondary palate, chickens have a natural cleft palate and turtles have primitive palate. These comparative studies will allow us to compare genes expressed in tissues surrounding the choanae and identify those that are correlated with a closed versus open palate. Next, I will culture the embryonic palate containing the choanae and will increase or decrease the levels of different signalling molecules that are enriched in this region. I will also implant microscopic foil barriers to block the choana signals from reaching the palate. The effect of these interventions on the breakdown of the oronasal membrane and the initiation of palatal shelves will be investigated. In chicken, the longer term effects on palatine bones will be studied by adding the signals or their inhibitors to the embryos while in the egg. These will be the first studies on the embryonic development of the choanae. The presence of a new signaling center in the face will be investigated, and novel molecular causes for facial abnormalities such as cleft palate will be discovered.