Koop Demian, Cisternas Paula, Morris Valerie B, Strbenac Dario, Yang Jean Yee Hwa, Wray Gregory A, Byrne Maria
School of Medical Science and Bosch Institute, The University of Sydney, Sydney, NSW, 2006, Australia.
School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW, 2006, Australia.
BMC Dev Biol. 2017 Feb 13;17(1):4. doi: 10.1186/s12861-017-0145-1.
The molecular mechanisms underlying the development of the unusual echinoderm pentameral body plan and their likeness to mechanisms underlying the development of the bilateral plans of other deuterostomes are of interest in tracing body plan evolution. In this first study of the spatial expression of genes associated with Nodal and BMP2/4 signalling during the transition to pentamery in sea urchins, we investigate Heliocidaris erythrogramma, a species that provides access to the developing adult rudiment within days of fertilization.
BMP2/4, and the putative downstream genes, Six1/2, Eya, Tbx2/3 and Msx were expressed in the earliest morphological manifestation of pentamery during development, the five hydrocoele lobes. The formation of the vestibular ectoderm, the specialized region overlying the left coelom that forms adult ectoderm, involved the expression of putative Nodal target genes Chordin, Gsc and BMP2/4 and putative BMP2/4 target genes Dlx, Msx and Tbx. The expression of Nodal, Lefty and Pitx2 in the right ectoderm, and Pitx2 in the right coelom, was as previously observed in other sea urchins.
That genes associated with Nodal and BMP2/4 signalling are expressed in the hydrocoele lobes, indicates that they have a role in the developmental transition to pentamery, contributing to our understanding of how the most unusual body plan in the Bilateria may have evolved. We suggest that the Nodal and BMP2/4 signalling cascades might have been duplicated or split during the evolution to pentamery.
棘皮动物独特的五辐射对称身体结构发育的分子机制，以及它们与其他后口动物两侧对称结构发育机制的相似性，对于追溯身体结构的进化具有重要意义。在这项关于海胆向五辐射对称转变过程中与Nodal和BMP2/4信号相关基因的空间表达的首次研究中，我们研究了红斑海胆（Heliocidaris erythrogramma），该物种在受精后数天内就能观察到发育中的成体原基。
BMP2/4以及假定的下游基因Six1/2、Eya、Tbx2/3和Msx在发育过程中五辐射对称的最早形态表现——五个水管叶中表达。前庭外胚层的形成，即覆盖左体腔并形成成体外胚层的特化区域，涉及假定的Nodal靶基因Chordin、Gsc和BMP2/4以及假定的BMP2/4靶基因Dlx、Msx和Tbx的表达。如在其他海胆中先前观察到的那样，Nodal、Lefty和Pitx2在右侧外胚层中表达，而Pitx2在右侧体腔中表达。
与Nodal和BMP2/4信号相关的基因在水管叶中表达，这表明它们在向五辐射对称的发育转变中发挥作用，有助于我们理解两侧对称动物中最独特的身体结构是如何进化的。我们认为，在向五辐射对称的进化过程中，Nodal和BMP2/4信号级联可能发生了复制或分裂。
