C. DEPARTMENT OF DEVELOPMENTAL GENETICS
C-d. Division of Physiological Genetics - Yukiko Gotoh Group

RESEARCH ACTIVITIES

(1) The Wnt-β-catenin pathway directs neuronal differentiation of cortical neural precursor cells

Yusuke Hirabayashi, Yasuhiro Itoh, Norihisa Masuyama and Yukiko Gotoh

--Neural precursor cells (NPCs) have the ability to self-renew and to give rise to neuronal and glial lineages. The fate decision of NPCs between proliferation and differentiation determines the number of differentiated cells and the size of each region of the brain. However, the signals that regulate the timing of neuronal differentiation remain unclear. Here we show that the Wnt signaling inhibits self-renewal capacity of mouse cortical NPCs, and instructively promotes their neuronal differentiation. Overexpression of Wnt7a or of a stabilized form of β-catenin in mouse cortical NPC culture induced neuronal differentiation even in the presence of FGF2, a self-renewal-promoting factor in this system. Moreover, blockade of the Wnt signaling led to inhibition of neuronal differentiation of cortical NPCs in the developing mouse neocortex. Furthermore, the β-catenin/TCF complex appears to directly regulate the promoter of neurogenin1, a gene implicated in cortical neuronal differentiation. Importantly, stabilized β-catenin did not induce neuronal differentiation of cortical NPCs at earlier developmental stages, consistent with previous reports, suggesting stage-specific functions of the Wnt signaling. Collectively, these results reveal pivotal physiological roles for the Wnt signaling in neuronal differentiation.

(2) Hes binding to STAT3 mediates crosstalk between Notch and JAK-STAT signaling

Sachiko Kamakura, Koji Oishi, Takeshi Yoshimatsu, Norihisa Masuyama and Yukiko Gotoh

--Although the Notch and JAK-STAT signaling pathways fulfill overlapping roles in growth and differentiation regulation, no coordination mechanism has been proposed to explain their relationship. Here we show that STAT3 is activated in the presence of active Notch as well as the Notch effectors Hes1 and Hes5. Hes proteins associate with JAK2 and STAT3, and facilitate complex formation between JAK2 and STAT3, thus promoting STAT3 phosphorylation and activation. Furthermore, suppression of endogenous Hes1 expression reduces growth factor induction of STAT3 phosphorylation. STAT3 appears to be essential for maintenance of radial glial cells and differentiation of astrocytes by Notch in the developing central nervous system. These results imply that direct protein-protein interactions coordinate cross-talk between the Notch-Hes and JAK-STAT pathways.

(3) Notch promotes survival of neural precursor cells via mechanisms distinct from those regulating neurogenesis Koji Oishi, Sachiko Kamakura, Yuko Isazawa, Takeshi Yoshimatsu, Keisuke Kuida, Norihisa Masuyama and Yukiko Gotoh

--During development of the mammalian brain, many neural precursor cells (NPCs) undergo apoptosis. The regulation of such cell death, however, is poorly understood. We now show that the survival of mouse embryonic NPCs in vitro was increased by culture at a high cell density and that this effect was attributable to activation of Notch signaling. Expression of an active form of Notch1 thus markedly promoted NPC survival. Hes proteins, key effectors of Notch signaling in inhibition of neurogenesis, were not sufficient for the survival-promoting effect of Notch1. This effect of Notch1 required a region of the protein containing the RAM domain and was accompanied by up-regulation of the anti-apoptotic proteins Bcl-2 and Mcl-1. Moreover, knockdown of these proteins by RNA interference resulted in blockade of the Notch1-induced survival. These results reveal a new function of Notch, the promotion of NPC survival.

(4) JNK promotes Bax translocation to mitochondria through phosphorylation of 14-3-3 proteins

Fuminori Tsuruta, Jun Sunayama, Yasunori Mori, Norihisa Masuyama and Yukiko Gotoh

--Targeted gene disruption studies have established that the c-Jun NH₂-terminal kinase (JNK) is required for the stress-induced release of mitochondrial cytochrome c and apoptosis, and that the Bax subfamily of Bcl-2-related proteins is essential for JNK-dependent apoptosis. However, the mechanism by which JNK regulates Bax has remained unsolved. Here we demonstrate that activated JNK promotes Bax translocation to mitochondria through phosphorylation of 14-3-3, a cytoplasmic anchor of Bax. Phosphorylation of 14-3-3 led to dissociation of Bax from this protein. Expression of phosphorylation-defective mutants of 14-3-3 blocked JNK-induced Bax translocation to mitochondria, cytochrome c release and apoptosis. Collectively, these results have revealed a key mechanism of Bax regulation in stress-induced apoptosis.

PUBLICATIONS

Papers

1. Hirabayashi, Y., Itoh, Y., Tabata, H., Nakajima, K., Akiyama, T., Masuyama, N. and Gotoh, Y. (2004). The Wnt-beta-catenin pathway directs neuronal differentiation of cortical neural precursor cells. Development, 131, 2791-2801.
2. Kamakura, S., Oishi, K., Yoshimatsu, T., Nakafuku, M., Masuyama, N. and Gotoh, Y. (2004). Hes binding to STAT3 mediates crosstalk between Notch and JAK-STAT signaling. Nat. Cell Biol. 6, 547-554.
3. Miyagi, S., Saito, T., Mizutani, K., Masuyama, N., Gotoh, Y., Iwama, A., Nakauchi, H., Masui, S., Niwa, H., Nishimoto, M., Muramatsu, M. and Okuda, A. (2004). The sox-2 regulatory regions display their activities in two distinct multipotent stem cells. Mol. Cell. Biol., 24, 4207-4220.
4. Oishi, K., Kamakura, S., Isazawa, Y., Yoshimatsu, T., Kuida, K., Nakafuku, M., Masuyama, N. and Gotoh, Y. (2004). Notch promotes survival of neural precursor cells via mechanisms distinct from those regulating neurogenesis. Dev. Biol., 276, 172-184.
5. Tsuruta, F., Sunayama, J., Mori, Y., Shimizu, S., Tsujimoto, Y., Yoshioka, K., Masuyama, N. and Gotoh, Y. (2004). JNK promotes Bax translocation to mitochondria through phosphorylation of 14-3-3 proteins. EMBO J. 23, 1889-1899.
6. Sunayama, J., Ando, Y., Itoh, N., Tomiyama, A., Sakurada, K., Sugiyama, A., Kang, D., Tashiro, F., Gotoh, Y., Kuchino, Y. and Kitanaka, C. (2004). Physical and functional interaction between BH3-only protein Hrk and mitochondrial pore-forming protein p32. Cell Death Differ. 11, 771-781.
7. Ogihara, T., Asano, T., Katagiri, H., Sakoda, H., Anai, M., Shojima, N., Ono, H., Fujishiro, M., Kushiyama, A., Fukushima, Y., Kikuchi, M., Noguchi, N., Aburatani, H., Gotoh, Y., Komuro, I. and Fujita, T. (2004). Oxidative stress induces insulin resistance by activating the nuclear factor-B pathway and disrupting normal subcellular distribution of phosphatidylinositol 3-kinase. Diabetologia 5, 794-805.

Reviews
8. 大石康二・後藤由季子（2004）脳発生と細胞死,実験医学 増刊,22 (11), pp1634-1639.
9. 大橋淳一郎,後藤由季子（2004）生存シグナル,生体の科学,55 (5), pp450-451.
10. 鎌倉幸子・吉松剛志,後藤由季子（2004）神経幹細胞の運命を制御するNotch-Hes経路とJAK-STAT3経路のクロストーク,実験医学,22 (15), pp2167-2170.

SOCIAL CONTRIBUTIONS AND OTHERS

Oncogene (Editor)
Journal of Biochemistry (Associate Editor)
Cell Structure and Function (Associate Editor)

各賞受賞
日本癌学会奨励賞受賞
日本女性科学者の会奨励賞受賞