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Development 129, 5205-5216 (2002)
Copyright © 2002 The Company of Biologists Limited

T-brain homologue (HpTb) is involved in the archenteron induction signals of micromere descendant cells in the sea urchin embryo

Takuya Fuchikami1, Keiko Mitsunaga-Nakatsubo1, Shonan Amemiya2, Toshiya Hosomi1, Takashi Watanabe1, Daisuke Kurokawa1,*, Miho Kataoka1, Yoshito Harada3, Nori Satoh3, Shinichiro Kusunoki4, Kazuko Takata1, Taishin Shimotori1, Takashi Yamamoto1, Naoaki Sakamoto1, Hiraku Shimada1 and Koji Akasaka1,{dagger}

1 Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
2 Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
3 Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
4 LSL, Nerima-ku, Tokyo 178-0061, Japan
* Present address: Evolutionary Regeneration Biology Group, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan

{dagger} Author for correspondence (e-mail: koji{at}hiroshima-u.ac.jp)

Accepted 30 July 2002

Signals from micromere descendants play a crucial role in sea urchin development. In this study, we demonstrate that these micromere descendants express HpTb, a T-brain homolog of Hemicentrotus pulcherrimus. HpTb is expressed transiently from the hatched blastula stage through the mesenchyme blastula stage to the gastrula stage. By a combination of embryo microsurgery and antisense morpholino experiments, we show that HpTb is involved in the production of archenteron induction signals. However, HpTb is not involved in the production of signals responsible for the specification of secondary mesenchyme cells, the initial specification of primary mesenchyme cells, or the specification of endoderm. HpTb expression is controlled by nuclear localization of ß-catenin, suggesting that HpTb is in a downstream component of the Wnt signaling cascade. We also propose the possibility that HpTb is involved in the cascade responsible for the production of signals required for the spicule formation as well as signals from the vegetal hemisphere required for the differentiation of aboral ectoderm.

Key words: Archenteron induction signal, T-brain, Sea urchin


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© The Company of Biologists Ltd 2002