@article{be66dc7d29344ff288d1c49c4f2bd4ca,
title = "Antagonizing activity of chick Grg4 against tectum-organizing activity",
abstract = "Alar plate of chick mesencephalon differentiates into the optic tectum. It has been shown that factors expressed in the mes-metencephalic boundary induce the tectum and give positional specificity. Chick Grg4 is expressed at first in the anterior neural fold. The expression localizes from the posterior diencephalon to the mesencephalon by stage 10. To investigate the function of Grg4 in mesencephalic development, Grg4 overexpression was carried out by in ovo electroporation. After Grg4 overexpression, expression of En-2, Pax5, Fgf8, and EphrinA2 was repressed, and Pax6 was upregulated in the mesencephalic region. Grg4 overexpression caused the morphological change; mesencephalic swelling became smaller and the di-mesencephalic boundary shifted posteriorly, that is, the anterior limit of tectum shifted posteriorly. Importantly, cotransfection of Grg4 with Pax5 canceled the tectum-inducing activity of Pax5. These results suggest that Grg4 works as an antagonist against tectum-organizing activity. It was also shown that transfected N-terminal domains of Grg4 induced En-2 expression. Since N- terminal domains were transported to the nucleus in the neuroepithelium, they could act as dominant negative for endogenous Grg4. These results indicate that Grg4 has repressing activity against the organizing molecules and suggest that Grg4 plays important roles in formation of anterior tectal boundary and polarity. (C) 2000 Academic Press.",
keywords = "Corepressor, En, Groucho, Mesencephalon, Organizer, Tcf, Tectum, β-catenin",
author = "Sayaka Sugiyama and Funahashi, {Jun Ichi} and Harukazu Nakamura",
note = "Funding Information: We thank Dr. K. Kitamura for the Otx2 probe, Dr. S. Noji for the Fgf8 probe, Dr. I. Araki for the Pax6 probe and the EphrinA2 probe, Dr. Y. Hamada for the Notch cDNA, Dr. K. Sakamoto for the Notch probe, Dr. H. C. Clevers for the Tcf1 cDNA, Dr. A. Nagafuchi for the β-catenin cDNA, Dr. H. Kondo for pMiwSV, and Dr. J. Kimura, Dr. I. Araki, and Dr. Y. Watanabe for their critical reading of the manuscript. This work was supported by the Ministry of Education, Culture and Sports, Japan; the Agency of Science and Technology, Japan; and Japan Small and Medium Enterprise Corpora- double-staining of Grg4 mRNA (blue) and En-2 protein (brown), the specimen was flat-mounted (I) and destained for Grg4 signal (I′). Weak expression of En-2 is induced by cotransfected β-catenin (black arrows). Higher magnifications show that repression of En-2 expression is weakened by cotransfection of the stabilized form of β-catenin (compare J and J′ with Figs. 3A1 and 3A′1). Scale bar is 200 µm for A–B′, G, and H; 100 µm for I and I′; 20 µm for J and J′; and 5 µm for C–F. FIG. 8. The repressing activity of Grg4 is independent of Notch signaling. (A–B) Enhanced Notch1 expression by Grg4 overexpression. (C–D) Expression of En-2 after transfection of constitutive active Notch1. After double-staining for Grg4 (red) and Notch1 (blue) by in situ hybridization (A), specimen was flat-mounted (B) and destained for Grg4 signal (B′). Higher magnifications of the flat-mounted specimen show that the sites of strong Notch1 expression correspond to the Grg4 overexpression (comparison of B with B′). After double-staining of Notch1 transcripts (blue) and En-2 protein (brown) by in situ hybridization and immunohistochemistry (C), a horizontal section was cut at the level indicated in C (D). Expression of En-2 is unaffected by constitutive active Notch1 (D1 and D2). Scale bar is 200 µm for A and C; 100 µm for D; and 20 µm for B, D1, and D2.",
year = "2000",
month = may,
day = "1",
doi = "10.1006/dbio.2000.9643",
language = "English",
volume = "221",
pages = "168--180",
journal = "Developmental Biology",
issn = "0012-1606",
publisher = "Academic Press Inc.",
number = "1",
}