Early Embryonic Axis Formation in a Simple Chordate Ascidian
Embryonic axes are established during early embryogenesis in animal development and serve as frameworks upon which embryonic body structures are built. A variety of tissue precursors are arranged along embryonic axes. Therefore, elucidation of the mechanisms by which these axes form in early embryos is fundamental in understanding how animal development proceeds, and this has become one of the most important questions in the field of developmental biology. In this chapter, axis formation mechanisms in the eggs and early embryos of marine invertebrates and simple chordates—ascidians—are presented. This information provides an opportunity to better understand the comprehensive and unique axis formation story of this particular animal species. However, generally important concepts of embryonic axis formation are interspersed throughout the axis-forming processes in ascidians. Therefore, readers should appreciate the complex and fascinating strategy underlying the establishment of early embryonic axes for the later development of ascidians and find the comparison of these mechanisms with those utilized in other organisms interesting.
KeywordsAnimal-vegetal Ascidian Ascidian Maternal determinant Dorsal-ventral Embryonic axis formation Left–right asymmetry Ooplasmic movements Postplasmic/PEM RNA
I would like to thank the members of the Nishida Lab at Osaka University and the researchers at the Asamushi Research Center for Marine Biology at Tohoku University for stimulating discussions.
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