Evolution of cis-regulatory modules for the head organizer gene goosecoid in chordates: comparisons between Branchiostoma and Xenopus

Background: In cephalochordates (amphioxus), the notochord runs along the dorsal to the anterior tip of the body. In contrast, the vertebrate head is formed anterior to the notochord, as a result of head organizer formation in anterior mesoderm during early development. A key gene for the vertebrate head organizer, goosecoid (gsc), is broadly expressed in the dorsal mesoderm of amphioxus gastrula. Amphioxus gsc expression subsequently becomes restricted to the posterior notochord from the early neurula. This has prompted the hypothesis that a change in expression patterns of gsc led to development of the vertebrate head during chordate evolution. However, molecular mechanisms of head organizer evolution involving gsc have never been elucidated.Results: To address this question, we compared cis-regulatory modules of vertebrate organizer genes between amphioxus, Branchiostoma japonicum, and frogs, Xenopus laevis and Xenopus tropicalis. Here we show conservation and diversification of gene regulatory mechanisms through cis-regulatory modules for gsc, lim1/lhx1, and chordin in Branchiostoma and Xenopus. Reporter analysis using Xenopus embryos demonstrates that activation of gsc by Nodal/FoxH1 signal through the 5′ upstream region, that of lim1 by Nodal/FoxH1 signal through the first intron, and that of chordin by Lim1 through the second intron, are conserved between amphioxus and Xenopus. However, activation of gsc by Lim1 and Otx through the 5′ upstream region in Xenopus are not conserved in amphioxus. Furthermore, the 5′ region of amphioxus gsc recapitulated the amphioxus-like posterior mesoderm expression of the reporter gene in transgenic Xenopus embryos.Conclusions: On the basis of this study, we propose a model, in which the gsc gene acquired the cis-regulatory module bound with Lim1 and Otx at its 5′ upstream region to be activated persistently in anterior mesoderm, in the vertebrate lineage. Because Gsc globally represses trunk (notochord) genes in the vertebrate head organizer, this cooption of gsc in vertebrates appears to have resulted in inhibition of trunk genes and acquisition of the head organizer and its derivative prechordal plate

ナメクジウオmyc遺伝子の進化的解析

The proto-oncogene myc is one of the most important genes controlling cell proliferation. The vertebrate genome has four myc genes (c-, N-, L-, s-myc), whose evolutionary origin and relationship are unclear. Here, we isolated a myc gene from a protochordate, the amphioxus Branchiostoma belcheri, which is thought to be the nonvertebrate that is closest to the vertebrates. A 1480 bp cDNA sequence was determined and contains an ATGinitiated ORF consisting of 371 amino acids. The exon/intron structure was conserved. Southern blotting and degenerate PCR showed that the amphioxus genome contained only a single myc gene. A phylogenetic tree of Myc family genes based on the deduced amino acid sequences indicated that amphioxus Myc was located outside the vertebrate Myc family. These results suggest that myc gene duplication occurred after protochordate on phylogeny.がん原遺伝子myc は細胞増殖を制御する重要な遺伝子の一つである。脊椎動物では4種類のmycが存在しているが，その起源や類縁関係は明らかとなっていない。本研究で我々は，脊椎動物に最も近縁の無脊椎動物であるナメクジウオBranchiostoma belcheriからmyc遺伝子を単離した。全長1480塩基対のcDNA は371アミノ酸からなるORFを含んでいた。また，エキソン／イントロン構造は保存されていた。サザンブロット法およびdegenerate PCRの結果，ナメクジウオのゲノムは単一のmyc 遺伝子を持つことが明らかとなった。また，推定アミノ酸配列に基づいた系統解析の結果，ナメクジウオMyc は脊椎動物Mycファミリーの外側に位置していた。これらの結果から，myc ファミリーは原索動物以降に形成されたものと考えられた。東京海洋大学海洋科学部海洋生物資源学科東京海洋大学海洋科学部海洋生物資源学科コネチカット大学東京大学海洋研究所日本魚類生物科学研究所東京海洋大学海洋科学部海洋生物資源学

Changes in Specific Gonadotropin Binding Sites in the Liver during Metamorphosis in the Bullfrog, Rana catesbeiana(Endocrinology)

Volume: 8Start Page: 759End Page: 76