Duplication of an amphioxus myogenic bHLH gene is independent of vertebrate myogenic bHLH gene duplication

Evolutionary aspects of a new MyoD gene in amphioxus (Branchiostoma belcheri) and its promoter specificity in skeletal and cardiac muscles

“…All current data support a theory proposed by Araki et al (1996), who suggested that there were independent gene duplications in amphioxus after divergence of amphioxus from vertebrate lineage that resulted in the production of multiple MyoD genes in amphioxus. One of the MyoD gene in amphioxus might represent the close relative of the ancestral myogenic gene that generated the four MRF genes in vertebrates by gene duplications at the origin of the vertebrates.…”

“…Based on this theory, Yuan et al (2003) proposed that the amphioxus genome contains only one myogenic bHLH gene named AmphiMDF, and the four myogenic genes in vertebrates were derived from the single ancestral gene (AmphiMDF) through these two rounds of genome wide duplications. Results from our study and those by other authors (Araki et al 1996;Schubert et al 2003) have shown that there are multiple myogenic genes in amphioxus, and the AmphiMDF genes appeared to be generated after the divergence of amphioxus from vertebrates, thus, they argue against the above-mentioned hypothesis.…”

“…These investigators further proposed that AmphiMDF was the ancestral myogenic gene of vertebrate MRFs (Yuan et al 2003). In contrast, two other studies have demonstrated that there are at least two MyoD family members in amphioxus Branchiostoma floridae and B. belcheri (Araki et al 1996;Schubert et al 2003). The two MyoD genes exhibited partially overlapping patterns of expression in the paraxial mesoderm and developing somites in amphioxus embryos as well as they also exhibited their unique patterns of expression (Schubert et al 2003).…”

“…However, the function of MRFs appears to be conserved during evolution because the sea urchin MRF gene could activate muscle programming in mice (Venuti et al 1991). The four myogenic genes in vertebrates are believed to have been generated by gene duplication from one ancestor gene in invertebrates during the chordate evolution (Atchley et al 1994;Araki et al 1996). The evolutionary history of MRF gene duplications, is, however, still unclear.…”

Phylogenetic analysis and expression patterns of <I>tropomyosin</I> in amphioxus

“…的机制。 从胚胎发育过程来看文昌鱼具有和脊椎动物 一样的分节过程。原肠运动后, 脊椎动物 (爪蛙除 外) 胚胎的肌肉发生也是从位于脊索两侧的近轴中 胚层按从前到后的顺序分节 (segmentation)、成团, 逐渐形成一定数目的体节 (somites), 再由体节分 化出 3 种不同的组织：生骨节、生肌节、生皮节, 将 来分别生成骨骼、肌肉以及真皮和结缔组织 (Mei & Ding,1999)。 从分子水平上看，有相同的基因和蛋白参与了 文昌鱼和脊椎动物的肌肉发育过程，如碱性肌球蛋 白轻链和肌动蛋白不仅存在于脊椎动物中, 也同样 存在于文昌鱼中 (Holland, 1995;Kusakabe, 1997)。 MyoD、Myf5、肌细胞生成素 (myogenin) 和 MRF4 是控制脊椎动物肌肉细胞决定和分化的关键因子 (Braun et al, 1989;Davis et al, 1987;Simon & Konieczny, 1989;Wright et al, 1989;Yun, 1996), 能 激活一系列肌肉专一因子的表达, 从而促使细胞向 肌细胞方向分化。作为一种最接近脊椎动物的头索 动物, 文昌鱼在其基因组中有两个生肌 bHLH 基因 片 段 (Araki, 1994(Araki, , 1996Beach, 1999;Meedel, 1997) 。 对 两 个 文 昌 鱼 MyoD 基 因 家 族 基 因 AmphiMRF1 和 AmphiMRF2 进行转录表达研究发现 两 者 最 初 均 在 近 轴 中 胚 层 中 表 达 , 其 中 AmphiMRF1 的 表 达 时 间 比 AmphiMRF2 稍 晚 (Schubert et al, 2003)。 脊索是脊椎动物门胚胎的一个中轴性结构。在 较高等的脊椎动物中, 脊索是一个瞬时存在的结构, 它定位于胚胎的中间, 与背腹轴与左右的轴极性形 成相关。脊索产生一些分泌因子, 给其周围的组织 以信号, 提供其定位和命运分化的信息 (Christ et al, 2004;Danos & Yost, 1995;Fouquet et al, 1997;Goldstein & Fishman, 1998;Lohr et al, 1997;Munsterberg & Lassar, 1995;Pourquié et al, 1993;Yamada et al, 1991Yamada et al, , 1993 Neighbor-joining tree was constructed using sequence 1-240 from the alignment in Fig.4 and 1 000 bootstrap replicates with the treepuzzle program. The Suberites domuncula Tropomyosin was used as out-group.…”