Ovule is a lateral organ finally differentiated from the terminating floral meristem in rice |
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Authors: | Yamaki Shinichiro Nagato Yasuo Kurata Nori Nonomura Ken-ichi |
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Institution: | aCenter of Molecular Brain Physiology, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany;bInstitute for Populationgenetics, University of Veterinary Medicine Vienna, Veterinärplatz 1, 1210 Vienna, Austria |
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Abstract: | Cranial placodes are specialized ectodermal regions in the developing vertebrate head that give rise to both neural and non-neural cell types of the neuroendocrine system and the sense organs of the visual, olfactory and acoustic systems. The cranial placodes develop from a panplacodal region which is specifically marked by genes of the eyes absent/eya and two “six homeobox” family members (sine oculis/six1 and six4). It had been believed that cranial placodes are evolutionary novelties of vertebrates. However, data from non-vertebrate chordates suggest that placode-like structures evolved in the chordate ancestor already. Here, we identify a morphological structure in the embryonic head of the beetle Tribolium castaneum with placode-like features. It is marked by the orthologs of the panplacodal markers Tc-six4, Tc-eya and Tc-sine oculis/six1 (Tc-six1) and expresses several genes known to be involved in adenohypophyseal placode development in vertebrates. Moreover, it contributes to both epidermal and neural tissues. We identify Tc-six4 as a specific marker for this structure that we term the insect head placode. Finally, we reveal the regulatory gene network of the panplacodal genes Tc-six4, Tc-eya and Tc-six1 and identify them as head epidermis patterning genes. Our finding of a placode-like structure in an insect suggests that a placode precursor was already present in the last common ancestor of bilaterian animals. |
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Keywords: | Cranial placodes Six4 Six1 Sine oculis Eya neuroendocrine Insect head Tribolium |
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