Morov Arseniy R, Ukizintambara Tharcisse, Sabirov Rushan M, Yasui Kinya
Department of Biological Science, Graduate School of Science, Hiroshima University, 1-3-1, Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan Department of Zoology and General Biology, Institute of Fundamental Medicine and Biology, Kazan (Volga Region) Federal University, 18 Kremlyovskaya Street, Kazan 420008, Republic of Tatarstan, Russian Federation.
Department of Biological Science, Graduate School of Science, Hiroshima University, 1-3-1, Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
Open Biol. 2016 Jun;6(6). doi: 10.1098/rsob.160062.
Acquisition of dorsal structures, such as notochord and hollow nerve cord, is likely to have had a profound influence upon vertebrate evolution. Dorsal formation in chordate development thus has been intensively studied in vertebrates and ascidians. However, the present understanding does not explain how chordates acquired dorsal structures. Here we show that amphioxus retains a key clue to answer this question. In amphioxus embryos, maternal nodal mRNA distributes asymmetrically in accordance with the remodelling of the cortical cytoskeleton in the fertilized egg, and subsequently lefty is first expressed in a patch of blastomeres across the equator where wnt8 is expressed circularly and which will become the margin of the blastopore. The lefty domain co-expresses zygotic nodal by the initial gastrula stage on the one side of the blastopore margin and induces the expression of goosecoid, not-like, chordin and brachyury1 genes in this region, as in the oral ectoderm of sea urchin embryos, which provides a basis for the formation of the dorsal structures. The striking similarity in the gene regulations and their respective expression domains when comparing dorsal formation in amphioxus and the determination of the oral ectoderm in sea urchin embryos suggests that chordates derived from an ambulacrarian-type blastula with dorsoventral inversion.
获取背侧结构，如脊索和中空神经索，可能对脊椎动物的进化产生了深远影响。因此，脊椎动物和海鞘中对脊索动物发育过程中的背侧形成进行了深入研究。然而，目前的认知并不能解释脊索动物是如何获得背侧结构的。在此，我们表明文昌鱼保留了回答这个问题的关键线索。在文昌鱼胚胎中，母源节点信使核糖核酸（mRNA）根据受精卵中皮质细胞骨架的重塑而不对称分布，随后，左撇子基因首先在赤道两侧的一群卵裂球中表达，在这些卵裂球中，Wnt8呈环状表达，且这些卵裂球将形成胚孔的边缘。到原肠胚初期，左撇子基因表达区域在胚孔边缘的一侧与合子节点基因共同表达，并在该区域诱导鹅膏蕈氨酸、非典型、脊索蛋白和短尾蛋白1基因的表达，就像在海胆胚胎的口外胚层中一样，这为背侧结构的形成提供了基础。比较文昌鱼的背侧形成与海胆胚胎口外胚层的确定过程中，基因调控及其各自表达区域的显著相似性表明，脊索动物起源于具有背腹反转的步带型囊胚。
