Department of Biological, Sciences, California State University Long Beach, 1250 Bellflower Blvd, Long Beach, CA 90815, USA.
Evodevo. 2012 Sep 3;3(1):19. doi: 10.1186/2041-9139-3-19.
The gastrula stage represents the point in development at which the three primary germ layers diverge. At this point the gene regulatory networks that specify the germ layers are established and the genes that define the differentiated states of the tissues have begun to be activated. These networks have been well-characterized in sea urchins, but not in other echinoderms. Embryos of the brittle star Ophiocoma wendtii share a number of developmental features with sea urchin embryos, including the ingression of mesenchyme cells that give rise to an embryonic skeleton. Notable differences are that no micromeres are formed during cleavage divisions and no pigment cells are formed during development to the pluteus larval stage. More subtle changes in timing of developmental events also occur. To explore the molecular basis for the similarities and differences between these two echinoderms, we have sequenced and characterized the gastrula transcriptome of O. wendtii.
Development of Ophiocoma wendtii embryos was characterized and RNA was isolated from the gastrula stage. A transcriptome data base was generated from this RNA and was analyzed using a variety of methods to identify transcripts expressed and to compare those transcripts to those expressed at the gastrula stage in other organisms.
Using existing databases, we identified brittle star transcripts that correspond to 3,385 genes, including 1,863 genes shared with the sea urchin Strongylocentrotus purpuratus gastrula transcriptome. We characterized the functional classes of genes present in the transcriptome and compared them to those found in this sea urchin. We then examined those members of the germ-layer specific gene regulatory networks (GRNs) of S. purpuratus that are expressed in the O. wendtii gastrula. Our results indicate that there is a shared 'genetic toolkit' central to the echinoderm gastrula, a key stage in embryonic development, though there are also differences that reflect changes in developmental processes.
The brittle star expresses genes representing all functional classes at the gastrula stage. Brittle stars and sea urchins have comparable numbers of each class of genes and share many of the genes expressed at gastrulation. Examination of the brittle star genes in which sea urchin orthologs are utilized in germ layer specification reveals a relatively higher level of conservation of key regulatory components compared to the overall transcriptome. We also identify genes that were either lost or whose temporal expression has diverged from that of sea urchins.
原肠胚期是三个初级胚层分化的发育阶段。此时，指定胚层的基因调控网络已经建立，并且定义组织分化状态的基因已经开始被激活。这些网络在海胆中已经得到了很好的描述，但在其他棘皮动物中却没有。脆星虫 Ophiocoma wendtii 的胚胎与海胆胚胎有许多共同的发育特征，包括间充质细胞的内陷，这些细胞产生胚胎骨骼。值得注意的是，在分裂过程中没有形成微细胞，在发育到幼体阶段也没有形成色素细胞。发育事件的时间也发生了更微妙的变化。为了探索这两种棘皮动物之间的相似性和差异性的分子基础，我们对 O. wendtii 的原肠胚转录组进行了测序和特征描述。
描述了脆星虫胚胎的发育过程，并从原肠胚期分离 RNA。从该 RNA 生成转录组数据库，并使用多种方法对其进行分析，以识别表达的转录本，并将这些转录本与其他生物体中原肠胚期表达的转录本进行比较。
使用现有的数据库，我们鉴定了脆星虫转录本，这些转录本对应于 3385 个基因，包括 1863 个与海胆 Strongylocentrotus purpuratus 原肠胚转录组共享的基因。我们描述了转录组中存在的基因的功能类别，并将其与在这种海胆中发现的基因进行了比较。然后，我们检查了 S. purpuratus 中在 O. wendtii 原肠胚中表达的特定于胚层的基因调控网络（GRN）的成员。我们的结果表明，在棘皮动物原肠胚这一胚胎发育的关键阶段，存在一个共同的“遗传工具包”，尽管也存在反映发育过程变化的差异。
脆星虫在原肠胚期表达所有功能类别的基因。脆星虫和海胆具有相同数量的每种类别基因，并且在原肠胚期有许多共同表达的基因。检查脆星虫中用于胚层指定的海胆同源基因揭示了与整个转录组相比，关键调节成分的相对较高水平的保守性。我们还鉴定了那些丢失或其时间表达已经与海胆分化的基因。
