A Gbx homeobox gene in amphioxus: Insights into ancestry of the ANTP class and evolution of the midbrain/hindbrain boundary
A Gbx homeobox gene in amphioxus: Insights into ancestry of the ANTP class and evolution of the midbrain/hindbrain boundary
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DOI：
10.1016/j.ydbio.2006.03.003
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发表时间：
2006-07-01
影响因子：
2.7
通讯作者：
Holland, Linda Z.
中科院分区：
文献类型：
--
作者：
Castro, L. Filipe C.;Rasmussen, Stacy L. K.;Holland, Linda Z.
在脊椎动物中枢神经系统（CNS）中，后部表达的Gbx2和前部表达的OtX2之间的相互拮抗作用定位了中脑/后脑边界（MHB），但不诱导MHB组织者基因，例如En、Pax2/5/8和Wnt1。在头索类文昌鱼的 CNS 中，Otx 也在前端表达，但 En、Pax2/5/8 和 Wnt1 在 Otx 尾端附近不表达，这引发了关于文昌鱼中是否存在 MHB 组织者的疑问。为了研究 MHB 的进化起源，我们克隆了单个文昌鱼 Gbx 基因。荧光原位杂交表明，与脊椎动物一样，文昌鱼 Gbx 和 Hox 簇位于同一染色体上。通过对连锁基因的分析，我们认为在进化过程中，脊椎动物的单个祖先 Gbx 基因复制了四倍，随后丢失了两个重复项。文昌鱼 Gbx 在胚胎后部 75% 的所有胚层中表达，在 CNS 中，Gbx 和 Otx 结构域毗邻脑泡（前脑/中脑）和后脑之间的边界。因此，定位 MHB 的遗传机制存在于脊椎动物的原索动物祖先中，但不足以诱导组织者基因。与半索动物的比较表明，前 Otx 和后 Gbx 域可能在祖先后口动物中重叠，并且在 MHB 组织者特性进化之前，在脊索动物谱系的早期就与 MHB 邻接。 (c) 2006 Elsevier Inc. 保留所有权利。
In the vertebrate central nervous system (CNS), mutual antagonism between posteriorly expressed Gbx2 and anteriorly expressed OtX2 positions the midbrain/hindbrain boundary (MHB), but does not induce MHB organizer genes such as En, Pax2/5/8 and Wnt1. In the CNS of the cephalochordate amphioxus, Otx is also expressed anteriorly, but En, Pax2/5/8 and Wnt1 are not expressed near the caudal limit of Otx, raising questions about the existence of an MHB organizer in amphioxus. To investigate the evolutionary origins of the MHB, we cloned the single amphioxus Gbx gene. Fluorescence in situ hybridization showed that, as in vertebrates, amphioxus Gbx and the Hox cluster are on the same chromosome. From analysis of linked genes, we argue that during evolution a single ancestral Gbx gene duplicated fourfold in vertebrates, with subsequent loss of two duplicates. Amphioxus Gbx is expressed in all germ layers in the posterior 75% of the embryo, and in the CNS, the Gbx and Otx domains abut at the boundary between the cerebral vesicle (forebrain/midbrain) and the hindbrain. Thus, the genetic machinery to position the MHB was present in the protochordate ancestors of the vertebrates, but is insufficient for induction of organizer genes. Comparison with hemichordates suggests that anterior Otx and posterior Gbx domains were probably overlapping in the ancestral deuterostome and came to abut at the MHB early in the chordate lineage before MHB organizer properties evolved. (c) 2006 Elsevier Inc. All rights reserved.