Okafuji T, Funahashi J, Nakamura H
Department of Molecular Neurobiology, Institute of Development, Aging and Cancer (IDAC), Tohoku University, Seiryo-machi 4-1, Aoba-ku, Sendai, 980-8575, Japan.
Brain Res Dev Brain Res. 1999 Aug 5;116(1):41-9. doi: 10.1016/s0165-3806(99)00073-5.
Transplantation experiments have shown that the mes-metencephalic boundary (isthmus) acts as an organizer for the development of the optic tectum. We have cloned Pax-2 which is expressed in the isthmus. Previously it was shown that Pax-5, a member of the same Pax subfamily as Pax-2, transformed the diencephalon into a tectum-like structure and induced isthmus- and tectum-related genes both in the mesencephalon and in the diencephalon. In order to define the distinct roles between Pax-2 and Pax-5 in development of the tectum, we expressed Pax-2 ectopically in the mesencephalon and the diencephalon of E2 chick embryos by in ovo electroporation. Histological observation demonstrated that Pax-2 transformed the diencephalon into a tectum-like structure. In Pax-2, transfected embryos the expression of isthmus- and tectum-related genes such as Fgf8 and En-2 was induced in the diencephalon. However, neither Fgf8 nor En-2 expression was induced in the mesencephalon, making a striking contrast with the result of Pax-5 misexpression. In E2 chick embryos, the mesencephalon is committed of its fate to differentiate into the tectum, but the diencephalon has plasticity on its fate. Moreover, Pax-2 expression in the isthmus precedes Pax-5 expression. Taking these results into consideration, it is suggested that Pax-2 plays a crucial role in initiation of the tectal development, and that Pax-5 functions to maintain the state of tectal differentiation.
移植实验表明，中脑-后脑边界（峡部）在视顶盖的发育过程中起到组织者的作用。我们克隆了在峡部表达的Pax-2。此前研究表明，Pax-5与Pax-2属于同一Pax亚家族成员，它能将间脑转化为类似顶盖的结构，并在中脑和间脑中诱导与峡部和顶盖相关的基因表达。为了明确Pax-2和Pax-5在顶盖发育过程中的不同作用，我们通过鸡胚卵内电穿孔技术，在E2期鸡胚的中脑和间脑中异位表达Pax-2。组织学观察显示，Pax-2能将间脑转化为类似顶盖的结构。在转染了Pax-2的胚胎中，间脑中诱导了Fgf8和En-2等与峡部和顶盖相关基因的表达。然而，中脑中既未诱导Fgf8表达，也未诱导En-2表达，这与Pax-5错误表达的结果形成了鲜明对比。在E2期鸡胚中，中脑已注定分化为顶盖，但其命运已确定，而间脑在其命运上具有可塑性。此外，峡部中Pax-2的表达先于Pax-5的表达。综合这些结果表明，Pax-2在顶盖发育的起始阶段起着关键作用，而Pax-5的功能是维持顶盖分化的状态。
