| Although the condition of the deep-sea hydrothermal vent is harsh,a vigorousecosystem is supported by the symbiosis between the chemoautotrophicmicroorganisms and their hostes.The creasures living there have possessed the uniquemechanism to adapt to the extreme environment.The special ecosystem is not onlypotential biological resource,but also arises the though of scientists about the lifeorigin,evolution,adaptation to the extreme environments and so on.Ridgeia piscesae,living around the hydrothermal vent of Juan de Fuca Ridge,isan ideal model for studying the adaptative mechanism to extreme environment.Forinsights of its molecular characteristics,a SMART cDNA library of 5.71×10~6 cloneswas constructed.The average length of the inserted cDNA fragments is about 1.0 kbp.A total of 879 clones were picked at random and sequenced.199 genes wereidentified for the first time.They were found to be related to basal metabolism,cytoskeleton and membrane proteins,adaptation and defense,cell proliferation,signaltransduction,DNA replication,transcription and translation and so on.Among them,we found 23 various chitin-binding proteins consist of different chitin bindingdomains and a chitinase that only contain a domain of GH18 (glycosyl hydrolasesfamily 18).Additionally,high polymorphism also exists in other genes,such asmyohemerythrin,lysozyme that maybe a muti-funtional gene.The gene-expressionprofile might help to further understand the molecular basis of tube worm physiology.It will also lay a good foundation for functional studies on the adaptation to extremeenvironments and help to make use of them. MicroRNAs (miRNAs)are a class of small noncoding RNA that are 20-22nucleotides (nts)and function as regulators of gene expression.They were extensivelystudied and it was found that they were involved in various developmental andphysiological processes,such as cell differentiation,proliferation,apoptosis,development,virus defense and so on.Shrimp is one of the most important species inthe aquaculture.However,few studies about microRNA in shrimp were performed.In this study,we present the molecular characteristics of the molecules in themicroRNA pathway from Marsupenaeus japonicus.Argonaute is one of the mostimportant components in this pathway,which constitutes the RISC (RNA-inducedsilencing complex)with other partners and guides microRNAs to regulate theexpression of the target genes.Firstly,we present the molecular characteristics of theargonaute named Mjago from M.japonicus.Sequence analysis revealed that Mjagohad the conserved domains of the argonaute family:PAZ and PIWI.And it had theclose evolutionary relationship with argonaute 1 from arthropod,especially theargonaute 1 of Penaeus monodon.As shown in RT-PCR,Mjago appeared in everytissues examined and had the highest transcriptional level in the hemocyte.Moreover,during the white spot syndrome virus (WSSV)infection,it is found that thetranscriptional level of Mjago increased rapidly,but reduced after 48 h post infection.Furthermore,the study on the molecular characteristics of microRNA from M.japonicus was performed.For investigation on their relationship to the shrimpimmunity,the WSSV infected hemocytes were collected for isolation and clone ofsmall RNA.35 microRNAs were identified by the PCR method.Sequence analysisrevealed that some microRNAs shown the differential expression and evolutionalconservation.They have high homology with the microRNAs from other organisms,especially the arthropod,such as Drosophila melanogaster,Bombyx mori and so on.The result of semi-quantitative PCR showed that the expression of some microRNA changed during the WSSV infection.The study revealed that the molecules of the microRNA pathway from M.japonicus had the close relationship with the WSSV infection.Further study on theirindividual functions will be helpful to understand the molecular mechanism ofmicroRNA in the shrimp immunity and provide a clue for researches on shrimpimmunity against virus.
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