Hex - a Homeobox Gene Essential for Liver Development

Hex - 肝脏发育必需的同源框基因

• 批准号: 7345637
• 负责人: CLIFFORD W BOGUE
• 金额: $ 20.99万
• 依托单位: YALE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-09-30 至 2009-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7345637
• 关键词: Adult; Bile Duct Epithelium; Biliary; Biliary Atresia; Biliary Tract Diseases; Cell Therapy; Cells; Cyst; Defect; Development; Ductal; Employee Strikes; Essential Genes; Family member; Genes; Genetic; Hepatic; Hepatocyte; Homeobox; Homeobox Genes; Knock-out; Knockout Mice; Knowledge; Liver; Liver diseases; Morphogenesis; Mouse Strains; Mus; Numbers; Pathogenesis; Play; Pregnancy; Research; Role; Staging; Testing; base; bile duct; biliary tract; chicken DcoHalpha protein; insight; malformation; null mutation; polycystic liver disease; segregation

Both we and others have shown that mice with a null mutation of the homeobox gene Hhex die mid-gestation with multiple developmental defects, including complete absence of the liver (REF). The early lethality and absence of liver bud formation makes analysis of the role of Hhex in later stages of liver development and function impossible. We have shown that Hhex is expressed throughout liver development and in the adult liver in hepatoblasts, mature hepatocytes and both intra- and extra-hepatic bile duct epithelia (BDE), indicating that Hhex plays a role at multiple stages of liver morphogenesis (REF). To determine the role that Hhex plays in liver development after the formation of a liver bud, we generated mice a "conditional knockout" of Hhex. Using two strains of Hhex conditional knockout mice, we have demonstrated that Hhex has important functions after the formation of the liver bud. First, we found that Foxa3-Cre;Hhex?2,3/- mice, in which Hhex is deleted in early hepatoblasts at E8.5 - 9.0, die by E18.5 and have a liver that is significantly hypoplastic and composed predominately of bile ducts with a paucity of hepatocytes. Second, we found that AFP-Cre;Hhex?2,3/- mice, in which Hhex is deleted in the liver at E10.5 and later, have ductal plate malformations and polycystic livers. Based on the striking features of these two mouse strains, we hypothesize that 1) Hhex is required for the normal segregation of hepatoblasts into hepatocytes and bile duct epithelia (BDE); 2) enlarged bile ducts and biliary cysts develop in the absence of Hhex because Hhex is required for ductal plate remodeling and/or the normal development and function of BDE in the mature liver; and 3) Hhex regulates the expression of a number of liver-enriched genes during liver development and biliary cystogenesis. Those genes include the critically important HNF family members HNF6, HNF1a and HNF4a as well as other factors. In order to test these hypotheses, we propose the following 3 specific aims. Specific Aim 1. To determine if alterations in Hhex expression levels in hepatoblasts perturbs their normal differentiation into hepatocytes and BDE. Specific Aim 2. Determine the mechanism(s) involved in the formation of enlarged bile ducts and biliary cysts in Foxa3-Cre; Hhex?2,3/- and AFP-Cre; Hhex?2,3/- mice. Specific Aim 3. Elucidate the transcriptional network regulated by Hhex during liver and biliary tract development. The developmental mechanisms elucidated by these studies will provide knowledge that is critical to the identification of genetic factors required to generate differentiated cells for cell therapy of liver diseases. Additionally, this research will shed important insight into the pathogenesis of diseases of the biliary tract, including biliary atresia and polycystic liver disease.

我们和其他人都表明，具有同源异型盒基因Hhex无效突变的小鼠在妊娠中期死亡，并伴有多种发育缺陷，包括肝脏完全缺失（REF）。早期致死性和肝芽形成的缺乏使得分析Hhex在肝脏发育和功能的后期阶段中的作用成为不可能。我们已经表明，Hhex在整个肝脏发育过程中以及在成肝细胞、成熟肝细胞和肝内和肝外胆管上皮细胞（BDE）中的成人肝脏中表达，表明Hhex在肝脏形态发生（REF）的多个阶段发挥作用。为了确定Hhex在肝芽形成后肝脏发育中的作用，我们产生了Hhex的“条件性敲除”小鼠。使用两个品系的Hhex条件性基因敲除小鼠，我们已经证明了Hhex在肝芽形成后具有重要的功能。首先，我们发现Foxa 3-Cre;Hhex？在E8.5 - 9.0的早期成肝细胞中Hhex缺失的2，3/-小鼠在E18.5死亡，并且具有显著发育不良的肝脏，主要由胆管组成，肝细胞缺乏。其次，我们发现AFP-Cre;Hhex？在E10.5和更晚时肝脏中Hhex缺失的2，3/-小鼠具有导管板畸形和多囊肝。基于这两个品系小鼠的显著特征，我们假设：1）Hhex是肝母细胞正常分离成肝细胞和胆管上皮细胞（BDE）所必需的; 2）在没有Hhex的情况下，胆管和胆管囊肿的发展是因为Hhex是成熟肝脏中胆管板重塑和/或BDE正常发育和功能所必需的; 3）Hhex在肝脏发育和胆管囊肿形成过程中调节许多肝脏富集基因的表达。这些基因包括非常重要的HNF家族成员HNF 6，HNF 1a和HNF 4a以及其他因子。为了验证这些假设，我们提出了以下三个具体目标。具体目标1。确定成肝细胞中Hhex表达水平的改变是否会干扰其向肝细胞和溴化二苯醚的正常分化。具体目标2。确定Foxa 3-Cre; Hhex？2，3/-和AFP-Cre; Hhex？2.3只/-小鼠。具体目标3。阐明肝和胆道发育过程中Hhex调控的转录网络。这些研究阐明的发育机制将为识别产生用于肝病细胞治疗的分化细胞所需的遗传因子提供关键知识。此外，这项研究将揭示胆道疾病的发病机制，包括胆道闭锁和多囊肝病。