Molecular Genetics and Genomics杂志6月发表了中科院北京基因组研究所基因组科学及信息重点实验室与华东师范大学生命科学学院合作的研究成果Analysis and comparison of a set of expressed sequence tags of the parthenogenetic water flea Daphnia carinata。

隆线溞隶属节肢动物门(Arthropoda)、甲壳纲(Crustacea)、鳃足亚纲(Branchiopoda)、双甲目(Diplostraca)、枝角亚目(Cladocera)、溞科、溞属  。隆线溞有两种不同的生殖方式：孤雌生殖(单性生殖)与两性生殖。当外界条件比较适宜时，枝角类就行孤雌生殖。在环境条件恶化时，枝角类就行两性生殖，这时种群中不仅有雌体，同时还出现雄体，二者随即交配。两种生殖方式的交替，是枝角类对外界环境的一种特殊适应，孤雌生殖在有利环境下充分利用了条件，而两性生殖在不利环境下保证了种的生存与连续性。枝角类不但生殖方式特殊，还是一类重要的水生经济动物。它具有较高的蛋白质含量(占干重的40%-60%)，还含有水产经济类动物鱼、虾、蟹等生长发育所必需的氨基酸、维生素及钙质，是生产上十分理想的活体饵料，其产量与渔业生产关系密切。

科研人员对样品随机测序（5′端）3072条，一共得到3,040条高质量的EST序列，并最终得到1,495条unique sequences（465条contigs和1,030条singletons）。通过与公共数据库内的序列进行比对，总共注释了959个（64%）基因。通过基因表达丰度和功能分析（主要是GO和KEGG），对其基因表达谱特征有了全面的认识。其中与生殖和胚胎发育相关的基因共鉴定到57个基因，其中VTN和VTG基因所占比重较高；发现了生殖特异性表达的基因如ubulin  alpha  chain；另外检测到一些化学感应基因（CSP）和热激蛋白（HSP）基因。推测这些密切感受环境变化的基因在孤雌生殖中起到重要的作用，为以后克隆其全长基因序列并研究功能奠定了基础。

通过与近缘物种蚤状溞（Daphnia pulex）基因组序列的比对，比对之后得到1,283条（86%）unique  sequences与其基因组有较高的相似性。其中1,158条比对到基因的编码区域，另外有125条序列比对到基因间区或者内含子区。这些结果从侧面反映了水溞近缘种间（D. pulex和D. carinata）基因组序列、表达水平上的差异，为后续的比较基因组学分析提供了有力的支持。

推荐原始出处：

Mol Genet Genomics. 2009 May 26

Analysis and comparison of a set of expressed sequence tags of the parthenogenetic water flea Daphnia carinata.

Xu X, Song S, Wang Q, Qin F, Liu K, Zhang X, Hu S, Zhao Y.

Department of Life Science, East China Normal University, 200062, Shanghai, People's Republic of China.

The water flea Daphnia carinata (D. carinata) reproduces both sexually and parthenogenetically, yet little is known about the genes involved in these processes. To further clarify the reproductive biology of Daphnia and elucidate their unique mechanism of reproductive transformation, we have generated and characterized an expressed sequence tag (EST) data set from D. carinata. A set of 1,495 clusters were generated from sequencing 3,072 randomly chosen clones from a parthenogenetic, juvenile water flea cDNA library. The nucleic acid and deduced amino acid sequences were compared with known GenBank sequences. Functional annotation found that 959 clusters showed significant homology with known genes involved in a broad range of activities, including metabolism, translation, development and reproduction, as well as genes involved in sensing environmental factors. We speculate that genes involved in development and reproduction, along with genes that allow the organism to sense changes in the environment, play important roles in the process of parthenogenetic reproduction and could be markers of the early steps of sexual differentiation. Additionally, 86% of the D. Carinata unique sequences could be stringently mapped to the D. pulex genome, of which 125 mapped to intergenic and intronic regions on the current assembly. Our results provide practical insight into crustacean reproductive biology, in addition to establishing a new animal model for reproductive and developmental biology.