Mechanisms of early development in lancelets, protochordate

1.文昌鱼早期胚胎中β-Catenin的分布在受精卵细胞质中的β-Catenin首先定位于动物极，然后在卵裂过程中呈不对称分布，直至32细胞期。在64细胞期，所有的卵裂球都出现了最早的核定位。在原肠胚早期，虽然β-Catenin在背侧有集中表达，但Goosecoid和lhx 3的表达同时出现。用LiCl加热的胚胎显示β-Catenin在动物极周围的核中对称积累。2.文昌鱼早期胚胎的左右不对称性单卵联体双胞胎自发出现，LiCl诱导的背轴缺陷胚胎的pitx基因左侧表达正常。通过将受精卵暴露于电脉冲诱导的连体双胞胎在左侧个体的左侧和伴侣的右侧表达pitx。这些观察结果表明早期e ...更多信息 在文昌鱼胚胎中左右不对称的建立。当卵裂球在2-细胞期分离时，每个卵裂球都发育成正常但体积较小的胚胎。在这些胚胎中，pitx和nodal在左侧正常表达，少数例外。然而，大约一半的胚胎表现出两种基因的强表达，另一半则表现出弱表达。唯一的例外是双边表达。结果表明，左右决定早在文昌鱼胚胎的2-细胞期就开始了。3. soxC基因在神经板前半部分的表达我们分离了HMG家族的一个基因，并根据HMG结构域内的氨基酸序列和全序列分析了该基因与其他成员的关系。该基因位于C组簇内，称为soxC。在原肠胚中期，它首先在前神经板的前半部分表达。表达soxC的脑区可能在以后转化为脑泡。早期文昌鱼胚胎中的T-box基因从构建的早期原肠胚cDNA文库中克隆到5个T-box基因。它们是Tbrain/eomesodermin（Tbr/eomes）、bachyury 2、tbx 2/3、tbx 15/18/22和新鉴定的tbx 2/3/4/5。在分离的103个克隆中，Thr/eomes占95%。tbx 2/3/4/5在原肠胚早期的胚孔边缘有表达，在神经胚和早期仔鱼的原肠后端、神经肠管周围及神经肠管周围表皮均有表达。表达该基因的表皮细胞呈圆柱形，形成尾鳍，即单鳍。少

1.β-Catenin in the early lancelet embryoCytoplasmic β-Catenin was first localized to animal pole in fertilized eggs, and then distributed asymmetrically during cleaving until 32-cell stage. The furst nuclear localization occurred in all the blastomeres at the 64-cell stage. Although concentrated β-Catenin was found on the dorsal side at the early gastrula stage, expression of goosecoid and lhx3 appeared simultaneously. Embryos heated with LiCl showed showed symmetrical nuclear accumulation of β-Catenin around animal pole. However, these embryos developed correct dorso-ventral and left-right polarity.2.Left-right asymmetry in the early lancelet embryoMonozygotic conjoined twins arisen spontaneously and embryos with dorsal axis defects induced by LiCl showed normal left-sided expression of pitx. Conjoined twins induced by exposing fertilized eggs to an electric pulse expressed pitx on the left side of the left individual and on the right of the partner. These observations suggest early e … More stablishment of the left-right asymmetry in the lancelet embryo. When blastomeres were separated at the 2-cell stage, each developed into normal but small-sized embryo. In these embryos, pitx and nodal were expressed normally on the left side with a small number of exception. However, about a half of the embryos showed strong expression of both genes and the other half weak expression. The exception was bilateral expression. The results suggest that left-right determination starts as early as 2-cell stage in the lancelet embryo.3.Expression of soxC gene in anterior half of prospective neural plateA gene of the HMG family has been isolated and analyzed its relation with other members in tree patterns based on amino acid sequences within the HMG domain and whole sequences. The gene was located within the group C cluster and called soxC. It was first expressed in the anterior half of prospective neural plate at the mid-gastrula stage. The region that expressed soxC seems to transform into cerebral vesicle later. In the anterior expression region, pan-neural marker gene, neurogenein, is expressed soon, and posteriorly soxC-expressed zones of nenral plate differentiate cells expressing early neuronal marker genes.4.T-box genes in the early lancelet embryoForm a cDNA library constructed from early gastrulae, five T-box genes have been cloned. They are Tbrain/eomesodermin (Tbr/eomes), bachyury2, tbx2/3, tbx15/18/22, and newly identified tbx2/3/4/5. Among the 103 clones isolsted, Thr/eomes occupied 95%. Expression of tbx2/3/4/5 appeared at blastopore margin at the initial gastrula stage and was observed posterior end of archenteron, around neurenteric canal, and epidermis overlying the region of neurenteric canal in neurulae and early larvae. The epidermal cells expressing the gene became columner shape and formed tail fin that is sole fin developed in lancelets. Less