Mechanism for the involvement of the endothelin system in craniofacial and cardiovascular development

我们已经证明，从鳃上皮到间质的ET-1（内皮素-1）信号对神经嵴细胞中表达的ETAR（ETA受体）起重要作用。该通路调控Dlx5/6作为其下行同源基因，在第一鳃弓中起背-腹侧模式的作用。换句话说，我们已经证明，妊娠中期胚胎的背侧和腹侧第一鳃弓都被确定为上颌模式，但只有腹侧部分接收到ET-1-ETAR-Dlx5/6信号来指定下颌模式。然后我们将转基因基因敲入到ETAR基因位点的小鼠。为此，将突变体lox序列插入ETAR基因位点，以允许Cre重组酶介导的盒式交换。ETAR突变体lox纯合子的表型与ET-1或ETAR纯合子的表型相同。然后我们将LacZ基因敲入这些小鼠的ETAR启动子的下游。因此，ET-1信号参与支气管弓和心血管发育的靶细胞可见。这些小鼠使我们能够追踪心血管发育的过程，并分析神经嵴细胞与其他细胞之间的相互作用。进一步的敲入研究有望揭示鳃弓和心血管发育的分子机制。

We have demonstrated that the ET-1(endothelin-1) signal from branchial epithelium to mesenchyme is important to act on the ETAR(ETA receptor) expressed in the neural crest cells. This pathway regulates Dlx5/6 as homeotic gene which is down-steam of its pathway, and plays a role of dorso-ventral patterning in the 1st branchial arch. In other words, we have demonstrated that both dorsal and ventral 1st branchial arch is determined to be upper jaw pattern at the midgestation embryo, but only the ventral portion receives the ET-1-ETAR-Dlx5/6 signal to specify the lower pattern. Then we made the mice in which transgene can be knocked-in into the ETAR gene locus. For this purpose, mutant lox sequences were inserted into the ETAR gene locus to allow Cre recombinase-mediated cassette exchange. The phenotype of ETAR-mutant lox homozygotes are the same as the phenotype of ET-1 or ETAR homozygotes. We then knocked in the LacZ gene into the downstream of ETAR promoter in these mice. Consequently, target cells of the ET-1 signal contributed to branchial arch and cardiovascular development were visualized. These mice enable us to trace the process of cardiovascular development and to analyze of mutual interaction between neural crest cells and other cells. Further knock-in studies are expected to reveal the molecular mechanism underlying branchial arch and cardiovascular development.