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The micro1 gene is necessary and sufficient for micromere differentiation and mid/hindgut-inducing activity in the sea urchin embryo

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Abstract

In the sea urchin embryo, micromeres have two distinct functions: they differentiate cell autonomously into the skeletogenic mesenchyme cells and act as an organizing center that induces endomesoderm formation. We demonstrated that micro1 controls micromere specification as a transcriptional repressor. Because micro1 is a multicopy gene with at least six polymorphic loci, it has been difficult to consistently block micro1 function by morpholino-mediated knockdown. Here, to block micro1 function, we used an active activator of micro1 consisting of a fusion protein of the VP16 activation domain and the micro1 homeodomain. Embryos injected with mRNA encoding the fusion protein exhibited a phenotype similar to that of micromere-less embryos. To evaluate micro1 function in the micromere, we constructed chimeric embryos composed of animal cap mesomeres and a micromere quartet from embryos injected with the fusion protein mRNA. The chimeras developed into dauerblastulae with no vegetal structures, in which the micromere progeny constituted the blastula wall. We also analyzed the phenotype of chimeras composed of an animal cap and a mesomere expressing micro1. These chimeras developed into pluteus larvae, in which the mesomere descendants ingressed as primary mesenchyme cells and formed a complete set of skeletal rods. The hindgut and a part of the midgut were also generated from host mesomeres. However, the foregut and nonskeletogenic mesoderm were not formed in the larvae. From these observations, we conclude that micro1 is necessary and sufficient for both micromere differentiation and mid/hindgut-inducing activity, and we also suggest that micro1 may not fulfill all micromere functions.

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Acknowledgements

We thank Hiroshi Kubota for the Hpoe monoclonal antibody, Hideki Katow for the P4 monoclonal antibody, and Masato Kiyomoto for supplying the mature adult H. pulcherrimus.

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Authors and Affiliations

  1. Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, 920-1192, Japan

    Atsuko Yamazaki, Rika Kawabata, Kosuke Shiomi & Masaaki Yamaguchi

  2. Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwanoha, Kashiwa, 277-8562, Japan

    Shonan Amemiya

  3. Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan

    Masaya Sawaguchi & Keiko Mitsunaga-Nakatsubo

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  1. Atsuko Yamazaki
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  2. Rika Kawabata
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  3. Kosuke Shiomi
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  4. Shonan Amemiya
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  5. Masaya Sawaguchi
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  6. Keiko Mitsunaga-Nakatsubo
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  7. Masaaki Yamaguchi
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Correspondence to Masaaki Yamaguchi.

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Communicated by N. Satoh.

A. Yamazaki and R. Kawabata contributed equally to this study

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Yamazaki, A., Kawabata, R., Shiomi, K. et al. The micro1 gene is necessary and sufficient for micromere differentiation and mid/hindgut-inducing activity in the sea urchin embryo. Dev Genes Evol 215, 450–459 (2005). https://doi.org/10.1007/s00427-005-0006-y

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