Roles of Pax-2 in initiation of the chick tectal development

• Published in: Brain research. Developmental brain research Vol. 116; no. 1; pp. 41 - 49
• Main Authors: Okafuji, Tatsuya, Funahashi, Jun-ichi, Nakamura, Harukazu
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 05.08.1999
• Subjects: Amino Acid Sequence; Animals; Chick embryo; Chick Embryo - growth & development; Chick Embryo - metabolism; Cloning, Molecular; Diencephalon - embryology; Diencephalon - metabolism; DNA-Binding Proteins - genetics; Gene Expression Regulation, Developmental - physiology; Isthmus; Mesencephalon - embryology; Mesencephalon - metabolism; Molecular Sequence Data; Optic tectum; Organizer; Pax-2; Pax-5; PAX2 Transcription Factor; Sequence Homology, Amino Acid; Superior Colliculi - embryology; Superior Colliculi - metabolism; Transcription Factors - genetics; Transformation, Genetic; Chick embryo; Optic tectum; Pax-2; Isthmus; Pax-5; Organizer
• ISSN: 0165-3806
• 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.