DIX5 HOMEOBOX GENE CONTROL OF CRANIOFACIAL MORPHOGENESIS

哺乳动物头面部的胚胎发育是一个复杂的胚胎学过程，在分子水平上还知之甚少。在胚胎早期，哺乳动物的头面部首先表现为由成对的臂弓组成的胚胎样结构，该结构由原始的神经嵴来源的间充质细胞组成。这些神经脊细胞在从后脑迁移之前获得了一些图案信息，在它们迁移到颧弓的过程中，额外的图案信息被传授给它们。已经确定了几种含有同源异型盒的DNA结合转录调控因子，它们指导着颅面部区域的形态发生和细胞分化的某些方面。在这里，我们描述了一个Dlx5，一个新的含有同源异型盒的基因，远端少(DLX)家族，它在发育中的颅面部区域的间质中表达最强。根据其胚胎表达模式和其他DLX同源框基因的作用方式，Dlx5有可能成为颧弓结构正常形态发生和细胞分化的主要指导因子。为了了解颅面部胚胎发育的遗传学基础，我们建议改变同源盒Dlx5的正常功能，该同源盒在颧弓(以及所有骨骼元素的软骨膜区域)中显示高度受限的表达。此外，我们还将鉴定和鉴定在发育中的颅面部区域控制Dlx5基因表达的DNA顺式调控元件。为此，我们将主要依靠我们在过去八年中开发和改进的转基因小鼠技术。因此，(I)我们将产生Dlx5的中断(基因敲除)。(Ii)我们将确定控制Dlx5头面部特异基因表达的DNA调控元件。这些实验结果将有助于阐明Dlx5在正常颅面形态发生中的作用。这与我们的长期目标是了解指导哺乳动物颅面发育的分子机制是一致的，相信这些知识最终将被用来纠正颅面部区域的创伤或遗传缺陷。

Fetal development of the mammalian craniofacial region is a complex embryological process which is poorly understood at the molecular level. Early in embryonic life the mammalian craniofacial region is first manifested as a blastema-like structure of paired branchial arches comprised primary of neural crest-derived mesenchymal cells. These neural crest cells acquires some of their patterning information prior to emigration from the hindbrain, and additional patterning information is imparted to them during their migration into the branchial arches. Several homeobox-containing DNA-binding transcriptional regulations have been identified which direct certain aspects of the morphogenesis and cellular differentiation of the craniofacial region. Here we describe a Dlx5 a new homeobox-containing gene of the distal less (Dlx) family which is most strongly expressed in the mesenchyme of the developing craniofacial region. Based upon its embryonic expression pattern, and the mode of action of other Dlx homeobox-contain genes, Dlx5 has the potential of being a major director normal morphogenesis and cellular differentiation of branchial arch derived structures. To understand the genetic basis of embryonic development of the craniofacial region, we propose to alter the normal function of the homeobox Dlx5 which shows highly restricted expression in the branchial arches (as well as the perichondrial region of all skeletal elements). In addition, we will identify and characterize the DNA cis-regulatory elements which direct regionally-restricted Dlx5 gene expression in the developing craniofacial region. To this end, we will rely primarily on the transgenic mouse technology that we have developed and refined over the last eight years. Accordingly, (I) we will generate a disruption (gene knock-out) of Dlx5. (II) We will determine the DNA regulatory elements which control Dlx5 craniofacial-specific gene expression. Results of these experiments will help clarify the role of Dlx5 in normal craniofacial morphogenesis. This is in keeping with our long range goal which is to understand the molecular mechanisms involved in directing mammalian craniofacial development with the belief that such knowledge will eventually be used to correct either trauma to, or genetic defects of the craniofacial region.