倒立水母Cassiopea andromeda的POU、Hox基因家族的多样性及系统发育分析

Evolutionary of POU,Hox gene families of the upside-down jellyfish Cassiopea andromeda

与其他钵水母相比,倒立水母具有独特行为:在生命周期的大部分时间里,它都在海底呈倒立附着、“睡眠”的状态。为探索与这一独特行为相关的遗传信息,本研究对安朵仙水母(Cassiopea andromeda)和同属于钵水母纲的海蜇(Rhopilema esculentum)、巴布亚硝水母(Mastigias papua)进行首次全基因组测序、拼接和注释,并重点分析了这3种钵水母与感觉功能、神经系统发育相关的重要转录调节因子Hox和POU基因家族的多样性与系统发育关系。遗传分析显示,刺胞动物门中Hox和POU基因家族具有明显的物种间差异性。对Hox基因的分析首次发现钵水母及水螅(Hydra vulgaris)的“前段Hox基因”产生了部分缺失,并进一步印证了刺胞动物不存在“中段Hox基因”的假说。安朵仙水母和海蜇具有相对全面的ParaHox基因种类,即GSX和XLOX/CDX基因,而巴布亚硝水母只有GSX基因。在POU基因多样性方面,安朵仙水母、海蜇、星状海葵(Nematostella vectensis)的基因组具有全部4类POU,而巴布亚硝水母、海月水母(Aurelia aurita)、水螅只有2类POU。在本研究分析的刺胞动物中,安朵仙水母的POU-1,-6亚型的核苷酸多态性最高;安朵仙水母与指形鹿角珊瑚(Acropora digitifera)、星状海葵的POU-2/3/5亚型的序列多样性较其他钵水母更高。另外,3种钵水母与水螅粘附蛋白的比较结果表明,安朵仙水母具有巴布亚硝水母和海蜇所不具有的粘附相关鼠李糖结合凝集素和一类抗氧化活性物质铁螯合物还原酶。综上所述,安朵仙水母具有更多POU编码基因和复杂POU亚型,以及具有粘附相关凝集素和还原酶的编码基因,可能是与安朵仙水母倒立附着生活方式相关的关键遗传信息。

Cassiopea jellyfish is the so called“upside-down”jellyfish due to an unique behavior among scyphozoans and it remains inverted position and sedentary throughout the majority of their lifecycles on the sea bottom.To discover the genomic information related to this unique behavior,we sequenced and compared the draft genomes of the upside-down jellyfish Cassiopea andromeda and Mastigias papua,Rhopilema esculentum from the same class of Scyphozoa alongside orthologs of other cnidarians.Genetic analysis revealed the diversity and phylogeny of cnidarian essential regulators Hox,POU domain genes associating with jellyfish sense and nerve.This study supported the hypothesis that there is no central Hox gene in cnidarians and found that there is a partial deletion of anterior Hox gene during the evolution of Scyphozoa and H.vulgaris.As for ParaHox in cnidarians,GSX and XLOX/CDX genes were all found in C.andromeda and R.esculentum,though M.papua possessed only GSX gene.C.andromeda,R.esculentum and N.vectensis were found to have all 4 classes of POU genes while M.papua,A.aurita and H.vulgaris had only 2 POU gene classes,respectively.Among the cnidarians analyzed in this study,C.andromeda had the highest levels of nucleotide polymorphisms of the POU-1,-6 subtypes while C.Andromeda,with higher diversity of POU-2/3/5 domain gene class,was closer to the corals and sea anemones than other scyphozoans.The parallels and differences of the adhesive-related proteins between three scyphozoans and H.vulgaris were summarized.C.andromeda was predicted to have unique adhesive-related lectins(Rhamnose-binding lectin protein)and ferric-chelate reductase which M.papua and R.esculentum did not.In summary,greater numbers of POU encoding genes and more complex POU isoforms maybe one of the key genetic factors that contribute to the upside-down,“sleep-like”state of C.andromeda.The result that adhesive-related lectin proteins and reductase encoding genes remain in C.andromeda may be another potential genetic factor.