Formery L, Peluso P, Rank D R, Rokhsar D S, Lowe C J
Department of Biology, Hopkins Marine Station, Stanford University, 120 Oceanview Blvd, Pacific Grove, CA, 93950, USA.
Department of Cell and Molecular Biology, University of California Berkeley, Berkeley, CA, USA.
Evodevo. 2025 May 31;16(1):7. doi: 10.1186/s13227-025-00244-8.
Although the adult pentaradial body plan of echinoderms evolved from a bilateral ancestor, identifying axial homologies between the morphologically divergent echinoderms and their bilaterian relatives has been an enduring problem in zoology. The expression of conserved bilaterian patterning genes in echinoderms provides a molecular framework for resolving this puzzle. Recent studies in juvenile asteroids suggest that the bilaterian antero-posterior axis maps onto the medio-lateral axis of the arms, perpendicular to the proximo-distal axis of each of the five rays of the pentaradial body plan. Here, we test this hypothesis in another echinoderm class, the ophiuroids, using the cosmopolitan brittle star Amphipholis squamata. Our results show that the general principles of axial patterning are similar to those described in asteroids, and comparisons with existing molecular data from other echinoderm taxa support the idea that medio-lateral deployment of the bilaterian AP patterning program across the rays predates the evolution of the asterozoans, and likely the echinoderm crown-group. Our data also reveal expression differences between A. squamata and asteroids, which we attribute to secondary modifications specific to ophiuroids. Together, this work provides important comparative data to reconstruct the evolution of axial properties in echinoderm body plans.
尽管棘皮动物的成年五辐射体型是从双侧对称的祖先演化而来的，但确定形态上差异很大的棘皮动物与其双侧对称亲属之间的轴向同源性，一直是动物学中一个长期存在的问题。棘皮动物中保守的双侧对称模式基因的表达为解决这一难题提供了一个分子框架。最近对幼年海星的研究表明，双侧对称的前后轴对应于臂的中外侧轴，垂直于五辐射体型的五条射线中每条射线的近远轴。在这里，我们使用广泛分布的脆星鳞蛇尾（Amphipholis squamata）在另一类棘皮动物——蛇尾纲中验证这一假设。我们的结果表明，轴向模式形成的一般原则与海星中描述的原则相似，并且与来自其他棘皮动物类群的现有分子数据进行比较后支持这样一种观点，即双侧对称的前后模式形成程序在射线间的中外侧部署早于海星类动物的演化，可能也早于棘皮动物冠群的演化。我们的数据还揭示了鳞蛇尾和海星之间的表达差异，我们将其归因于蛇尾纲特有的次生修饰。这项工作共同提供了重要的比较数据，以重建棘皮动物体型轴向特征的演化。
