GENETIC CASCADE UNDERLYING NOTOCHORD FORMATION IN ASCIDIAN EMBRYOS

脊索是脊索动物最显著的特征。本研究旨在探索海鞘胚胎中脊索形成的遗传级联机制。以前的研究大多来自我自己的实验室，研究表明，肠乔纳短臂基因在细胞期开始表达，并在脊索分化中起着至关重要的作用。在本研究中，我们研究了(1)导致Ci-Bra表达的Ci-Bra上游级联和(2)导致脊索形态形成的Ci-Bra下游级联：(1)Ci-Bra上游级联：在本研究中，我们明确了(1)母亲提供的β-catenin在受精后从细胞质转移到植物卵裂球的核中，并决定了内胚层的发育命运，(2)β-catenin触发了包括FOXD、ZicL和Fgf9/16/20在内的各种靶基因的激活，(3)FOXD是β-连环蛋白的直接靶标，在TH…中表达(4)ZicL位于FOXD下游，在32细胞期的脊索/神经索细胞中表达，该基因的功能对Ci-Bra的激活是必不可少的。因此，本研究揭示了Ci-Bra上游基因级联由β-catenin、FOXD、ZicL和Ci-Bra组成。(2)Ci-Bra下游级联：我们成功地分离和鉴定了Ci-Bra下游基因，包括Pickle、ERM、酪氨酸磷酸和cdc45。这些基因的5‘上游序列含有Ci-Bra蛋白结合序列，提示它们是Ci-Bra的直接靶标。当这些Ci-Bra下游基因的功能被抑制时，脊索细胞的收敛-伸展运动被禁止。因此，大多数Ci-Bra下游基因作为参与形态发生运动的成员。因此，本研究是海鞘胚胎中支持脊索形成的遗传级联的成果

Notochord is the most prominent feature of chordates. The present study aimed to explore the genetic cascade underlying notochord formation in ascidian embryos. Previous studies, mostly from my own laboratory, demonstrated that Brachyury gene of Ciona intestinalis (Ci-Bra) begins to be expressed at the 64-cell stage and plays-an essential role in the notochord differentiation. In the present study, we investigated (1) Ci-Bra upstream cascade which leads to the initiation of Ci-Bra expression and (2) Ci-Bra downstream cascade which leads to morphological formation of the notochord(1) Ci-Bra upstream cascade : In the present study, we make clear that (1) maternally supplied beta-catenin is translocated after fertilization from the cytoplasm into nuclei of vegetal blastomeres and specifies the endoderm developmental fate, (2) beta-catenin triggers the activation of various target genes including FoxD, ZicL, and Fgf9/16/20, (3) FoxD is a direct target of beta-catenin and is expressed in th … More e endoderm cells at the 16-and 32-cell stage, and the gene function is essential for Ci-Bra activation, (4) ZicL is downstream of FoxD and is expressed in notochord/nerve cord cells at the 32-cell stage, and this gene function is essential for Ci-Bra activation. Therefore, the present study has revealed that Ci-Bra upstream genetic cascade consists of beta-catenin, FoxD, ZicL and Ci-Bra in this order(2) Ci-Bra downstream cascade : We have succeeded in the isolation and characterization of Ci-Bra downstream genes including prickle, ERM, tyrosine phosphate, and cdc45. The 5' upstream sequences of these genes contain Ci-Bra protein binding sequences, suggesting that they are direct targets of Ci-Bra. When function of these Ci-Bra downstream genes is suppressed, convergent-extension movement of the notochord cells is prohibited. Therefore, most of the Ci-Bra downstream genes act as members involved in morphogenetic movementsThe present study is therefore an achievement of genetic cascade underlying the notochord formation in the ascidian embryo Less