The Study of Molecular Basis for Congenital Molformations Using Knockout Mice

为了阐明先天性畸形的分子基础，我们分析了msh类同源异型盒基因Msxl和Msx 2的敲除小鼠，这些基因被认为参与器官发生过程中的上皮-间充质相互作用。Msxl突变体的牙齿发育停滞在芽期是由于牙上皮和间充质之间的信号通路中断所致。由牙上皮分泌的BMP 4和FGF 4在Denal间充质中诱导的Msxl继而诱导牙间充质中的BMP 4、LEF 1和多配体蛋白聚糖1。Msx 2突变体显示釉质形成失败。突变体的第一个釉质结中细胞凋亡减少可能是这种发育异常的原因。信号通路，即，BMP 4 * Msx 2 * BMP 4 * 凋亡的存在被认为是成釉器正常发育所必需的。Msx 2突变体也表现出异常的骨和软骨形成。成骨细胞和破骨细胞数量减少， ...更多信息 突变体生长板和皮质骨厚度薄。成骨细胞分化标志物Cbfa 1、骨连接蛋白、Alp、骨桥蛋白、BSP和骨钙素的表达在突变体发育中的长骨中降低。软骨细胞分化标志物CoIII、CoIX、PTHrP和PTH/PTHrP受体的表达在突变体中也降低。msx 2可能在这些基因的转录调控中发挥重要作用。Msx 1-Msx 2双突变体表现为拇指发育不全、多指、并指、桡骨和胫骨缺失。在E10.5双突变体肢芽中，原位杂交检测不到Shh在极化活动区（ZPA）的表达，Fgf 4的表达从顶端外胚层嵴（AER）的后半部分转移到前半部分。Msx 1和Msx 2在Shh的上游发挥作用，是Shh在肢体ZPA中表达所必需的，而Bmp 4在双突变体中也未检测到在进行区前部的表达。这些基因的异常表达被认为是导致拇指发育不良、多指畸形以及桡骨和胫骨缺失的原因。在E13.5趾间区，Bmp 4表达明显降低，细胞凋亡受到抑制。趾间区细胞凋亡的抑制可导致多指畸形。Msx 1和Msx 2是Bmp 4在进展区前部和趾间区表达所必需的，并且信号通路，即，来自进行区和趾间区的AER* Msx 1和Msx 2 * BMP 4的BMP和FGF对正常肢体形成起作用。总之，Msxl和Msx 2被认为在器官发生期间的上皮-间充质相互作用中作为重要的信号介质起作用。少

To clarify the molecular basis for congenital malformations, we have analyzed knockout mice of the msh-class homeobox genes Msxl and Msx2 which are thought to be involved in epithelial-mesenchymal interaction during organogenesis. The developmental arrest at the bud stage in the teeth of Msxl mutants is caused by the interruption of signaling pathway between dental epithelium and mesenchyme. Msxl induced in the denal mesenchyme by BMP4 and FGF4 which are secreted from dental epithelium, in turn, induces BMP4, LEF1, and syndecan 1 in the dental mesenchyme. Msx2 mutants showed a failure of enamel formation. The reduced apoptosis in the first enamel knot of mutants seamed to be a cause of this developmental abnormality. The signaling pathway, i.e., BMP4*Msx2*BMP4*apoptosis exists and is considered to be essential for normal development of enamel organ. Msx2 mutants also manifested abnormal bone and cartilage formation. The number of osteoblasts and osteoclasts was deminished and the thick … More ness of growth plate and cortical bone was thin in the mutants. Expression of the differentiation markers for osteoblasts Cbfa1, osteonectin, Alp, osteopontin, BSP, and osteocalcin were decreased iii the developing long bone of the mutants. Expression of the differentiation markers for chondrocytes CoIII, CoIX, PTHrP, and PTH/PTHrP receptor were also reduced in the mutants. Msx2 may play an important role for the transcriptional regulation of these genes. Msx1-Msx2 double mutants manifested hypoplastic thumbs, polydactyly, syndactyly, and absence of radius and tibia. In E1O.5 double mutant limb bud, the expression of Shh in the zone of polarizing activity (ZPA) could not be deteced by in situ hybridization and Fgf4 expression was shifted from the posterior half of the apical ectodermal ridge (AER) to the anterior half. Msxl and Msx2 function upstream of Shh, and are required for the expression of Shh in the limb ZPA.Bmp4 expression in the anterior portion of the progress zone also could not be detected in double mutants. The abnormal expression of these genes is thought to cause hypoplastic thumbs, polydactyly, and absence of radius and tibia. Furthermore, Bmp4 expression was markedly reduced and inhibition of apoptosis was observed in E13.5 interdigital region of double mutants. Inhibition of apoptosis in interdigital region can cause polydactyly. Msxl and Msx2 are required for the Bmp4 expression in the anterior portion of progress zone and interdigital region, and the signal pathway, i.e., BMP and FGF from AER*Msx1 and Msx2*BMP4 in progress zone and interdigital region functions for normal limb formation. In summary, Msxl and Msx2 are thought to function as important signal mediators in the epithelial-mesenchymal interaction during organogenesis. Less