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首页> 外文期刊>American Zoologist >Homeobox genes, retinoic acid and the development and evolution of dual body plans in the ascidian Herdmania curvata
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Homeobox genes, retinoic acid and the development and evolution of dual body plans in the ascidian Herdmania curvata

机译：同源盒基因，视黄酸和海马Herdmania curvata中双体计划的发展与演变

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Ascidians, along with other urochordates, are the most evolutionary distant group from vertebrates to display definitive chordate-specific characters, such as a notochord, dorsal hollow nerve cord, pharynx and endostyle. Most solitary ascidians have a biphasic life history that has partitioned the development of these characters between a planktonic microscopic tadpole larva (notochord and dorsal nerve cord) and a larger sessile adult (pharynx and endostyle). Very little is known of the molecular axial patterning processes operating during ascidian postlarval development. Two axial patterning homeobox genes Otx and Cdx are expressed in a spatially restricted manner along the ascidian anteroposterior axis during embryogenesis and postlarval development (i.e., metamorphosis). Comparisons of these patterns with those of homologous cephalochordate and vertebrate genes suggest that the novel ascidian biphasic body plan was not accompanied by a deployment of these genes into new pathways but by a heterochronic shift in tissue-specific expression. Studies examining the role of all-trans retinoic acid (RA) in axial patterning in chordates also contribute to our understanding of the role of homeobox genes in the development of larval and adult ascidian body plans. Our studies demonstrate that RA does not regulate axial patterning in the developing ascidian larval neuroaxis in a manner homologous to that found in vertebrates. Although RA may regulate the expression of some ascidian homeobox genes, ectopic application of RA does not appear to alter the morphology of the larval CNS. However, treatment with similar or lower concentrations of RA, have a profound effect on postlarval development and the juvenile body plan. These changes are correlated to a dramatic reduction of Otx expression. Through these RA-induced effects we infer that while RA may regulate the expression of some homeobox genes during embryogenesis it has a far more dramatic impact on postlarval development where regulative processes predominate.
机译：海鞘与其他脊索动物一样，是距脊椎动物进化最远的群体，显示出特定的脊索动物特征，例如脊索动物，背侧中空神经索，咽部和内膜。大多数独居的海生动物都具有双相生活史，已经将这些特征的发展划分为浮游镜t幼虫（脊索和背神经索）和较大的无柄成虫（咽和子宫内膜）。很少有人了解海鞘后幼虫发育过程中的分子轴向构图过程。在胚胎发生和幼体发育（即变态）过程中，两个轴向模式的同源盒基因Otx和Cdx在空间上沿海鞘前后轴表达。这些模式与同源头孢酸盐和脊椎动物基因的模式比较表明，新的海生双相体计划并不伴随这些基因向新途径的部署，而是组织特异性表达的异时性转变。研究检查全反式维甲酸（RA）在脊索动物轴向模式中的作用的研究也有助于我们了解同源异型盒基因在幼虫和成年海马体计划发展中的作用。我们的研究表明，RA不能以与脊椎动物中发现的同源的方式调节正在发育的海生幼虫神经轴中的轴向模式。尽管RA可能调节某些海马同源盒基因的表达，但RA的异位应用似乎并未改变幼虫CNS的形态。但是，用相似或较低浓度的RA进行治疗对幼虫后发育和幼体计划有深远的影响。这些变化与Otx表达的急剧减少有关。通过这些RA诱导的作用，我们推断，尽管RA可能在胚胎发生过程中调节某些同源盒基因的表达，但它对幼虫后发育的影响更为显着，在幼虫后发育中，调节过程占主导。

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