Hopkins Marine Station, Department of Biology, Stanford University, 120 Ocean View Boulevard, Pacific Grove, CA 93950, USA.
Hopkins Marine Station, Department of Biology, Stanford University, 120 Ocean View Boulevard, Pacific Grove, CA 93950, USA.
Curr Biol. 2017 Jan 9;27(1):87-95. doi: 10.1016/j.cub.2016.10.047. Epub 2016 Dec 8.
Many animals are indirect developers with distinct larval and adult body plans [1]. The molecular basis of differences between larval and adult forms is often poorly understood, adding a level of uncertainty to comparative developmental studies that use data from both indirect and direct developers. Here we compare the larval and adult body plans of an indirect developing hemichordate, Schizocardium californicum [2]. We describe the expression of 27 transcription factors with conserved roles in deuterostome ectodermal anteroposterior (AP) patterning in developing embryos, tornaria larvae, and post-metamorphic juveniles and show that the tornaria larva of S. californicum is transcriptionally similar to a truncated version of the adult. The larval ectoderm has an anterior molecular signature, while most of the trunk, defined by the expression of hox1-7, is absent. Posterior ectodermal activation of Hox is initiated in the late larva prior to metamorphosis, in preparation for the transition to the adult form, in which the AP axis converges on a molecular architecture similar to that of the direct developing hemichordate Saccoglossus kowalevskii. These results identify a molecular correlate of a major difference in body plan between hemichordate larval and adult forms and confirm the hypothesis that deuterostome larvae are "swimming heads" [3]. This will allow future comparative studies with hemichordates to take into account molecular differences caused by early life history evolution within the phylum. Additionally, comparisons with other phyla suggest that a delay in trunk development is a feature of indirect development shared across distantly related phyla.
许多动物是间接发育的，具有明显的幼虫和成虫体式[1]。幼虫和成虫形式之间的差异的分子基础通常理解不足，这为使用间接和直接发育的数据进行比较发育研究增加了不确定性。在这里，我们比较了间接发育半索动物加利福尼亚沙蚕[2]的幼虫和成虫体式。我们描述了 27 种转录因子的表达，这些转录因子在蜕皮动物外胚层前后（AP）模式形成中具有保守作用，这些转录因子在发育胚胎、扭形幼虫和后变态幼体中表达，并表明加利福尼亚沙蚕的扭形幼虫在转录上与成年的截短版本相似。幼虫外胚层具有前分子特征，而大多数躯干，由 hox1-7 的表达定义，不存在。在后幼虫期，Hox 的后外胚层激活在变态前开始，为向成年形式的过渡做准备，在成年形式中，AP 轴收敛到类似于直接发育半索动物尾索动物的分子结构。这些结果确定了半索动物幼虫和成虫形式之间体式主要差异的分子相关性，并证实了后口动物幼虫是“游动头部”的假设[3]。这将允许未来对半索动物进行比较研究，以考虑到门内早期生活史进化引起的分子差异。此外，与其他门的比较表明，躯干发育的延迟是间接发育的一个特征，在远缘门中共享。
