59 resultados para amphioxus


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SPC2 and SPC3 are two members of a family of subtilisin-related proteases which play essential roles in the processing of prohormones into their mature forms in the pancreatic B cell and many other neuroendocrine cells. To investigate the phylogenetic origins and evolutionary functions of SPC2 and SPC3 we have identified and cloned cDNAs encoding these enzymes from amphioxus (Branchiostoma californiensis), a primitive chordate. The amino acid sequence of preproSPC2 contains 689 aa and is 71% identical to human SPC2. In contrast, amphioxus prproSPC3 consists of 774 aa and exhibits 55% identity to human SPC3. These results suggest that the primary structure of SPC2 has been more highly conserved during evolution than that of SPC3. To further investigate the function(s) of SPC2 and SPC3 in amphioxus, we have determined the regional expression of these genes by using a reverse transcriptase-linked polymerase chain reaction (RT-PCR) assay. Whole amphioxus was dissected longitudinally into four equal-length segments and RNA was extracted. Using RT-PCR to simultaneously amplify SPC2 and SPC3 DNA fragments, we found that the cranial region (section 1) expressed equal amounts of SPC2 and SPC3 mRNAs, whereas in the caudal region (section 4) the SPC2-to-SPC3 ratio was 5:1. In the mid-body sections 2 and 3 the SPC2-to-SPC3 ratio was 1:5. By RT-PCR we also determined that amphioxus ILP, a homologue of mammalian insulin/insulin-like growth factor, was expressed predominately in section 3. These results suggest that the relative levels of SPC2 and SPC3 mRNAs are specifically regulated in various amphioxus tissues. Furthermore, the ubiquitous expression of these mRNAs in the organism indicates that they are involved in the processing of other precursor proteins in addition to proILP.

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At head of title: Abdruck aus Anatomischer anzeiger ... 44 band, no. 19, 1913.

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文昌鱼长期作为脊索动物的祖先模型被研究。它与脊椎动物发育机制的比较为后者的发生和进化提供了大量证据。Wnt信号通路在动物胚胎发育中行使着多样而重要的功能:如胚胎轴系的建立,胚层分化,神经图式形成等。在腔肠动物胚胎发育的早期,Wnt/β-catenin主要参与动植物半球极性的形成和胚层分化——很可能是Wnt通路的祖先功能。而在高等脊椎动物胚胎发育的早期,Wnt/β-catenin通路对于背腹轴、前后轴和左右轴极性的建立发挥着至关重要的作用。我们的研究主要集中在文昌鱼Wnt/β-catenin信号通路的两种调节因子Dickkopf(Dkk)和Kremen,以探明这些Wnt信号调节因子的祖先功能,以及在脊椎动物中获得新功能的进化历程。分泌性蛋白Dkk是Wnt信号通路的抑制因子,协同它的高亲和性受体Kremen,在两栖类胚胎头部的发育中起着关键作用。基于脊椎动物Dkk和kremen的报道以及佛罗里达文昌鱼基因组序列信息,我们运用分子克隆的方法,得到白氏文昌鱼Dkk家族的两个基因:BbDkk124和BbDkk3,以及Kremen家族的5个基因:BbKremen-a,BbKremen-c,BbKremen-d,BbKremen-e,BbKremen-g,用整体胚胎原位杂交的方法研究了它们的表达图谱,并在293T细胞和非洲爪蟾胚胎这两个系统中检测了它们对Wnt信号活性的影响和胚胎发育表型的影响。结果表明文昌鱼Dkk和Kremen的表达区域与脊椎动物的同源基因并不相同,出现了较大分歧,但BbDkk124作为Wnt信号抑制因子的功能是保守的。Kremen家族的两个基因BbKremen-e和BbKremen-g在293T细胞内对Wnt通路的影响不显著,而在非洲爪蟾系统中,引起胚胎不同的畸形表型。我们的实验结果为脊椎动物Dkk和Kremen 基因家族的进化提供了一些资料。 此外我们还研究了文昌鱼GATA家族的基因,这个家族在脊椎动物和非脊椎动物的发育中行使重要的动能,在进化上也是非常保守的。脊椎动物的GATA基因分为两个亚群:GATA1/2/3和GATA4/5/6。通过生物信息分析,我们在文昌鱼的基因组中找到了三个GATA基因:一个GATA1/2/3亚家族基因,两个GATA4/5/6亚家族基因,另外还找到一个类GATA基因。我们克隆了白氏文昌鱼GATA123的一段序列并研究了它在早期胚胎发育中的特异性表达。结果表明GATA123在原肠胚的中内胚层表达,而在神经胚晚期和幼体早期,GATA123在脑泡和消化道中部区域表达。这种表达模式与头部发育的重要基因Otx相类似。我们的研究结果提示在文昌鱼脑泡的发育过程中GATA123和Otx很可能协同发挥着重要的作用。

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BRUNOL 蛋白又称CELF(CUG-BP and ETR3 like factor)是一种典型的RNA 结合蛋白,它的N 端含有两个连续的RNA 识别结构域(RNA recognition motif,RRM), C 端有一个RRM 结构域。主要参与对可变剪切、翻译、降解和编辑等基因表达转录后水平的调节。迄今在人类中已发现6 个Brunol 基因家族成员,即Brunol1-6;在非洲爪蟾中已发现了5 个:Brunol1-5。近期,我们克隆了爪蟾的Brunol1-5 并研究了它们在非洲爪蟾早期胚胎发育过程中的时空表达图式。结果显示,与以往研究结果一致, Brunol1 基因高量、特异地在神经管中表达,提示Brunol1 基因可能对于爪蟾的神经系统的发生和发育发挥着重要的作用。本实验利用Morpholino 和过表达等手段研究了爪蟾Brunol1 基因对于爪蟾早期胚胎发育的影响。结果显示,在下调和过表达Brunol 1 基因的情况下都会导致胚胎出现体轴弯曲,眼睛和头部发育不全等表型。而将 Brunol1 基因特异的Morpholino 与它的mRNA 共注射时可以明显挽救这一表型。我们通过原位杂交实验,检测了一些爪蟾神经系统的标记基因在Brunol1 过表达胚胎中的表达情况,结果发现过表达Brunol1 基因能显著地下调Krox-20, N-tubulin, Lhx2, Pax6 等的表达,而Sox2 和Otx2 的表达却未受影响。这说明Brunol1 的异常表达确实影响到了神经系统发育过程的信号调控网络,导致胚胎发育的畸形。该结果将有助于阐述Brunol1 基因对于脊椎动物神经系统发生的意义。肌动蛋白是一种分布广泛而且在进化上十分保守的蛋白,它是构成细胞骨架的关键组分。通常人们将肌动蛋白分成肌肉型和胞质型两种类型,它们各自行使着不同的功能。在此,我们通过对古老的脊索动物文昌鱼的肌动蛋白基因家族进行系统的分析发现,文昌鱼中该基因家族成员多达30 多个,而且它们中很多都有连锁现象;进化分析的结果显示,文昌鱼的肌动蛋白基因家族通过串联重复序列的复制发生扩增;从结构上看,它们的基因结构多样化, 包含2-7 个外显子;同时,我们还克隆了两个不同的文昌鱼肌肉型的肌动蛋白基因,并进一步比较了它们在文昌鱼早期胚胎中的表达图式。结果显示,这两个基因在表达上有着细微的差别,这提示文昌鱼肌动蛋白基因家族成员在功能上的分化。该结论将有助于阐述肌动蛋白基因家族的进化以及它们在脊索动物发育的中所扮演的功能。

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The endostyle of invertebrate chordates is a pharyngeal organ that is thought to be homologous with the follicular thyroid of vertebrates. Although thyroid-like features such as iodine-concentrating and peroxidase activities are located in the dorsolateral part of both ascidian and amphioxus endostyles, the structural organization and numbers of functional units are different. To estimate phylogenetic relationships of each functional zone with special reference to the evolution of the thyroid, we have investigated, in ascidian and amphioxus, the expression patterns of thyroid-related transcription factors such as TTF-2/MoxE4 and Pax2/5/8, as well as the forkhead transcription factors FoxQ1 and FoxA. Comparative gene expression analyses depicted an overall similarity between ascidians and amphioxus endostyles, while differences in expression patterns of these genes might be specifically related to the addition or elimination of a pair of glandular zones. Expressions of Ci-FoxE and BbFoxE4 suggest that the ancestral FoxE class might have been recruited for the formation of thyroid-like region in a possible common ancestor of chordates. Furthermore, coexpression of FoxE4, Pax2/5/8, and TPO in the dorsolateral part of both ascidian and amphioxus endostyles suggests that genetic basis of the thyroid function was already in place before the vertebrate lineage. (c) 2005 Wiley-Liss, Inc.

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The lancelet (amphioxus) embryo develops from a miolecithal egg and starts gastrulation when it is approximately 400 cells in size, in a fashion similar to that of some non-chordate deuterostomes. Throughout this type of gastrulation, the embryo develops characteristics such as the notochord and hollow nerve cord that commonly appear in chordates. beta-Catenin is an important factor in initiating body patterning. The behavior and developmental pattern of this protein in early lancelet development was examined in this study. Cytoplasmic beta-catenin was localized to the animal pole after fertilization and then was incorporated asymmetrically into the blastomeres during the first cleavage. Asymmetric distribution was observed at least until the 32-cell stage. The first nuclear localization was at the 64-cell stage, and involved all of the cells. At the initial gastrula stage, however, concentrated beta-catenin was found on the dorsal side. LiCl treatment affected the asymmetric pattern of beta-catenin during the first cleavage. LiCl also changed distribution of nuclear beta-catenin at the initial gastrula stage: distribution extended to cells on the animal side. Apparently associated with this change, expression domains of goosecoid, lhx3 and otx also changed to a radially symmetric pattern centered at the animal pole. However, LiCl-treated embryos were able to establish embryonic polarity. The present study suggests that in the lancelet embryo, polarity determination is independent of dorsal morphogenesis.

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Lancelets (amphioxus), although showing the most similar anatomical features to vertebrates, never develop a vertebrate-like head but rather several structures specific to this animal. The lancelet anatomical specificity seems to be traceable to early developmental stages, such as the vertebrate dorsal and anterior-posterior determinations. The BMP and Wnt proteins play important roles in establishing the early basis of the dorsal structures and the head in vertebrates. The early behavior of BMP and Wnt may be also related to the specific body structures of lancelets. The expression patterns of a dpp-related gene, Bbbmp2/4, and two wnt-related genes, Bbwnt7 and Bbwnt8, have been studied in comparison with those of brachyury and Hnf-3 beta class genes The temporal expression patterns of these genes are similar to those of vertebrates; Bbbmp2/4 and Bbwnt8 are first expressed in the invaginating primitive gut and the equatorial region. respectively, at the initial gastrula stage. However, spatial expression pattern of Bbbmp2/4 differs significantly from the vertebrate cognates. It is expressed in the mid-dorsal inner layer of gastrulae and widely in the anterior region, in which vertebrates block BMP signaling, The present study suggests that the lancelet embryo may have two distinct developmental domains from the gastrula stage, the domains of which coincide later with the lateral diverticular and the somitocoelomic regions. The embryonic origin of the anterior-specific structures in lancelets corresponds to the anterior domain where Bbbmp2/4 is continuously expressed.

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Mesoderm formation plays a crucial role in the establishment of the chordate body plan. In this regard, lancelet embryos develop structures such as the anteriorly extended notochord and the lateral divertecula in their anterior body. To elucidate the developmental basis of these structures, we examined the expression pattern of a lancelet twist-related gene, Bbtwist, from the late gastrula to larval stages. In late-gastrula embryos, the transcripts of Bbtwist were detected in the presumptive first pair of somites and the middorsal wall of the primitive gut. The expression of Bbtwist was then upregulated in the lateral wall of somites and the notochord. At the late-neurula stage, it was also expressed in the anterior wall of the primitive gut, as well as in the evaginating lateral diverticula. No signal was detected in the left lateral diverticulum when it was separated from the gut, while in the right one, the gene was expressed later during the formation of the head coelom in knife-shaped larvae, and in the anterior part of the notochord in the same larvae. In 36-h larvae, only faint expression was detected in the differentiating notochordal and paraxial mesoderm in the caudal region. These expression patterns suggest that Bbtwist is involved in early differentiation of mesodermal subsets as seen in Drosophila and vertebrates. The expression in the anterior notochord may be related to its anterior expansion. The expression in the anterior wall of the primitive gut and its derivative, the lateral diverticula, suggests that lancelets share the capability to produce a mesodermal population from the tip of the primitive gut with nonchordate deuterostome embryos. (C) 1998 Academic Press.

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Previously we suggested that four proteins including aldolase and triose phosphate isomerase (TPI) evolved with approximately constant rates over long periods covering the whole animal phyla. The constant rates of aldolase and TPI evolution were reexamined based on three different models for estimating evolutionary distances, It was shown that the evolutionary rates remain essentially unchanged in comparisons not only between different classes of vertebrates but also between vertebrates and arthropods and even between animals and plants, irrespective of the models used, Thus these enzymes might be useful molecular clocks for inferring divergence times of animal phyla, To know the divergence time of Parazoa and Eumetazoa and that of Cephalochordata and Vertebrata, the aldolase cDNAs from Ephydatia fluviatilis, a freshwater sponge, and the TPI cDNAs from Ephydatia fluviatilis and Branchiostoma belcheri an amphioxus, have been cloned and sequenced, Comparisons of the deduced amino acid sequences of aldolase and TPI from the freshwater sponge with known sequences revealed that the Parazoa-Eumetazoa split occurred about 940 million years ago (Ma) as determined by the average of two proteins and three models, Similarly, the aldolase and TPI clocks suggest that vertebrates and amphioxus last shared a common ancestor around 700 Ma and they possibly diverged shortly after the divergence of deuterostomes and protostomes.

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文昌鱼是头索动物,被认为是现存的与脊椎动物最接近的无脊椎动物,经常被看作是分析从无脊椎动物到脊椎动物进化过程的一种重要的模式动物。在本研究中,我们克隆了青岛文昌鱼的GDF8/11、ACTIVIN和NM23-Bbt2基因,并对这些基因在不同胚胎发育时期和不同成体组织中的表达情况进行了分析,同时分析了这些基因的进化情况。 文昌鱼GDF8/11的基因组全长为9.9 kb,包括五个外显子和四个内含子,比其他物种多出两个外显子和两个内含子。在多出的第三个内含子中,我们分离出一个可能的转座因子,这表明这个内含子可能来源于转座子。文昌鱼GDF8/11 cDNA编码一个419个氨基酸的前体多肽,这个前体多肽与软体动物、硬骨鱼类、鸟类和哺乳动物的MSTN以及哺乳动物和斑马鱼的GDF11具有高同源性。系统分析表明文昌鱼GDF8/11位于脊椎动物MSTN和GDF11的根部,这个结果证实MSTN/GDF11来源于同一个祖先基因,并且文昌鱼GDF8/11可能就是他们的共同祖先,产生MSTN和GDF11的基因复制事件发生在脊椎动物分离之前和文昌鱼与脊椎动物分离之后或者分离时。RT-PCR结果表明GDF8/11基因在新受精的细胞、早原肠胚和刀形胚胎中表达,这与哺乳动物中的情况不同。这表明GDF8/11在文昌鱼中除了调节肌肉生长外还可能拥有其他的功能。 文昌鱼ACTIVIN的基因组序列长为6.1 kb,启动子大约长为447 bp,其基因组包括两个外显子和一个内含子,外显子/内含子边界严格遵守GT…AG的原则。文昌鱼ACTIVIN基因编码一个410个氨基酸的前体蛋白,前体蛋白包括信号肽、N-末端结构域和C-末端结构域。文昌鱼ACTIVIN基因演绎的氨基酸序列与脊椎动物比较发现ACTIVIN基因比较保守,特别是C-末端生物活性区。系统进化分析表明脊椎动物和无脊椎动物的ACTIVIN基因分别聚在一起,文昌鱼的ACTIVIN则位于脊椎动物ACTIVIN分支的根部,这表明文昌鱼ACTIVIN基因可能是脊椎动物ACTIVIN同源基因的祖先基因。 文昌鱼NM23-Bbt2 cDNA包括一个编码171个氨基酸的开放阅读框,序列分析表明文昌鱼NM23-Bbt2与其他物种高度保守,他们都包含高度保守的基元,并且这些基元在NM23的功能中扮演着重要的角色。RT-PCR分析表明文昌鱼NM23-Bbt2在所检测的组织和胚胎发育时期中的非特异性的表达模式。系统分析表明脊椎动物和无脊椎动物NM23-H2分别聚在一起,而文昌鱼NM23-Bbt2位于脊椎动物NM23-H2分支的根部,这表明文昌鱼NM23-Bbt2可能是脊椎动物NM23-H2同源基因的祖先基因。从无脊椎动物到脊椎动物的基因组结构比较表明五个外显子和四个内含子的基因组结构可能产生在文昌鱼与脊椎动物分离之前。

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本论文主要对青岛文昌鱼(Branchiostoma belcheri tsingtauense)肌肉组织进行了酶组织化学实验和电镜观察,分离了青岛文昌鱼肌球蛋白重链基因异构体并将其重组表达;克隆了青岛文昌鱼新生肽链相关复合体α亚基基因,并检测了其时空表达情况。 根据NADH酶组化实验可以将文昌鱼的肌细胞分成两类,即蓝紫色、有氧代谢型的浅层肌和基本不着色、无氧代谢型的深层肌。电镜观察进一步验证了酶组化的结果,并首次发现浅层肌和中间肌细胞肌丝密度明显大于深层肌。而mATPase组化实验没能对肌纤维进行分类,这也许是由于实验的pH条件不是文昌鱼的肌纤维ATP酶活的pH;或者其很容易失活;或者该酶的活化需要不同于其它动物的金属离子的缘故。 克隆到三条对应于肌球蛋白重链尾部保守区的异构体,其中两条是首次报道。这三条异构体都属于II类肌球蛋白并和脊椎、无脊椎动物的多种类型的肌球蛋白分子有较高的同源性;利用原核表达系统对异构体进行重组表达,获得了可溶性的表达蛋白,为制备文昌鱼肌球蛋白特异性抗体打下了基础。 从青岛文昌鱼成体中分离到了新生肽链相关复合体α亚基的全长cDNA,并检测了其时空表达情况。对其cDNA 5’端的基因组序列进行预测和比较分析,没有发现肌肉特异性外显子的存在。

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Bien que partageant une homologie structurelle évidente, les membres antérieurs (MA) sont toujours différents des membres postérieurs (MP). Ceci suggère l’existence d’un programme générique de formation d’un membre, un bauplan, qui doit être modulé de façon spécifique pour engendrer cette différence antéro-postérieure de l’identité. Nous avons donc voulu identifier les mécanismes déployés durant l’évolution pour permettre la mise en place de l’identité des membres. Le laboratoire avait précédemment caractérisé, chez les souris où le gène Pitx1 est inactivé, une transformation partielle des MP en MA couplée à une perte de croissance. Nous avons donc cherché à comprendre les mécanismes en aval de Pitx1 dans la détermination de l’identité postérieure. Notre démarche nous a permis d’identifier les gènes affectés par la perte de Pitx1 dans les MP, où nous avons confirmé une dérégulation de l’expression de Tbx4. Tbx4 et Tbx5 sont des candidats évidents pour déterminer l’identité, leur expression étant restreinte aux MP et MA, respectivement, mais leur implication dans ce processus était sujette à controverse. Nous avons donc évalué l’apport de Tbx4 en aval de Pitx1 dans les processus d’identité en restaurant son expression dans les MP des souris Pitx1-/-. Ce faisant, nous avons pu montrer que Tbx4 est capable de pallier la perte de Pitx1 dans le MP, en rétablissant à la fois les caractères d’identité postérieure et la croissance. En parallèle, nous avons montré que Tbx5 était capable de rétablir la croissance mais non l’identité des MP Pitx1-/-, démontrant ainsi de façon définitive une propriété propre à Tbx4 dans la détermination de l’identité des membres postérieure. La caractérisation de l’activité transcriptionnelle de Tbx4 et Tbx5 nous a permis de mettre en évidence un domaine activateur conservé mais aussi un domaine spécifique à Tbx4, répresseur de la transcription. Par ailleurs, une mutation faux-sens de TBX4 dans les patients atteints du syndrome coxo-podo-patellaire, TBX4Q531R, inactive le domaine répresseur, empêchant la compensation de l’identité mais non de la croissance des MP dépourvus de Pitx1, démontrant l’importance de cette fonction dans l’identité postérieure. La caractérisation de l’activité répressive de Tbx4, qui se manifeste seulement dans les membres postérieurs démontre l’importance de cette fonction dans l’identité postérieure. Nous avons aussi été en mesure d’identifier un corépresseur qui est suffisant pour supporter cette activité de Tbx4. Enfin, nous avons pu aussi démontrer l’activité transcriptionnelle d’un représentant du gène ancestral, présent chez Amphioxus, qui se comporte strictement comme un activateur et semble dépourvu du domaine répresseur. En somme, nous avons précisé le rôle de Tbx4 et Tbx5, ainsi que leur mécanisme, dans la détermination de l’identité des membres. Globalement, nos travaux permettent d’élaborer une théorie où une divergence d’activité transcriptionnelle de Tbx4 et Tbx5 est responsable de l’identité des membres et même entrevoir que cette divergence d’activité soit à la base de son apparition durant l’évolution.

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The Fox genes are united by encoding a fork head domain, a deoxyribonucleic acid (DNA)-binding domain of the winged-helix type that marks these genes as encoding transcription factors. Vertebrate Fox genes are classified into 23 subclasses named from FoxA to FoxS. We have surveyed the genome of the amphioxus Branchiostoma floridae, identifying 32 distinct Fox genes representing 21 of these 23 subclasses. The missing subclasses, FoxR and FoxS, are specific to vertebrates, and in addition, B. floridae has one further group, FoxAB, that is not found in vertebrates. Hence, we conclude B. floridae has maintained a high level of Fox gene diversity. Expressed sequence tag and complementary DNA sequence data support the expression of 23 genes. Several linkages between B. floridae Fox genes were noted, including some that have evolved relatively recently via tandem duplication in the amphioxus lineage and others that are more ancient.

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The endostyle of invertebrate chordates is a pharyngeal organ that is thought to be homologous with the follicular thyroid of vertebrates. Although thyroid-like features such as iodine-concentrating and peroxidase activities are located in the dorsolateral part of both ascidian and amphioxus endostyles, the structural organization and numbers of functional units are different. To estimate phylogenetic relationships of each functional zone with special reference to the evolution of the thyroid, we have investigated, in ascidian and amphioxus, the expression patterns of thyroid-related transcription factors such as TTF-2/MoxE4 and Pax2/5/8, as well as the forkhead transcription factors FoxQ1 and FoxA. Comparative gene expression analyses depicted an overall similarity between ascidians and amphioxus endostyles, while differences in expression patterns of these genes might be specifically related to the addition or elimination of a pair of glandular zones. Expressions of Ci-FoxE and BbFoxE4 suggest that the ancestral FoxE class might have been recruited for the formation of thyroid-like region in a possible common ancestor of chordates. Furthermore, coexpression of FoxE4, Pax2/5/8, and TPO in the dorsolateral part of both ascidian and amphioxus endostyles suggests that genetic basis of the thyroid function was already in place before the vertebrate lineage. (c) 2005 Wiley-Liss, Inc.

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The vertebrate Zic gene family encodes C2H2 zinc finger transcription factors closely related to the Gli proteins. Zic genes are expressed in multiple areas of developing vertebrate embryos, including the dorsal neural tube where they act as potent neural crest inducers. Here we describe the characterization of a Zic ortholog from the amphioxus Branchiostoma floridae and further describe the expression of a Zic ortholog from the ascidian Ciona intestinalis. Molecular phylogenetic analysis and sequence comparisons suggest the gene duplications that formed the vertebrate Zic family were specific to the vertebrate lineage. In Ciona maternal CiZic/Ci-macho1 transcripts are localized during cleavage stages by asymmetric cell division, whereas zygotic expression by neural plate cells commences during neurulation. The amphioxus Zic ortholog AmphiZic is expressed in dorsal mesoderm and ectoderm during gastrulation, before being eliminated first from midline cells and then from all neurectoderm during neurulation. After neurulation, expression is reactivated in the dorsal neural tube and dorsolateral somite. Comparison of CiZic and AmphiZic expression with vertebrate Zic expression leads to two main conclusions. First, Zic expression allows us to define homologous compartments between vertebrate and amphioxus somites, showing primitive subdivision of vertebrate segmented mesoderm. Second, we show that neural Zic expression is a chordate synapomorphy, whereas the precise pattern of neural expression has evolved differently on the different chordate lineages. Based on these observations we suggest that a change in Zic regulation, specifically the evolution of a dorsal neural expression domain in vertebrate neurulae, was an important step in the evolution of the neural crest.