Genes Expressed in the Amphioxus Notochord Revealed by EST Analysis

[摘要] Thenotochordcellofthecephalochordateamphioxusadultisuniqueduetotheoccurrenceofmyofilamentsinthecytoplasm.ThepresentEST(expressedsequencetag)analysistargetedmRNAsoftheamphioxusnotochordtodeterminegenesthatareexpressedthere.NotochordcellswereisolatedfromBranchiostomabelcheriadults,fromwhichacDNAlibrarywasconstructed.Analysisofasetof257ESTs(both5′and3′ends)showedthatabout11%ofthecDNAsarerelatedtomusclegenes,while9%ofthemaregenesforextracellularmatrixproteinsassociatedwithformationofthenotochordalsheath.Themuscle-relatedgenesincludedactin,tropomyosin,troponinI,myosinregulatorylightchain,myosinlightchainkinase,myosinheavychain,calmodulin,calponin,calciumvectorprotein,creatinekinase,muscleLIMprotein,andSH3-bindingglutamate-richprotein,suggestingthatvertebrateskeletalandsmoothmuscle-typegenesaresimultaneouslyexpressedintheamphioxusnotochord.NucleotidesequencesofcDNAsforactin,tropomyosin,troponinI,andafewotherswerecompletelydeterminedtosubstantiatetheconclusions.Thechordatemuscle-typeactinisdistinguishablefromthecytoplasmic-typeactinbytheusageofaminoacidresiduesat20diagnosticpositions.Interestingly,analysisoftheusageofaminoacidresiduesatthesepositionsshowedthatthe“amphioxusnotochordactin”isauniqueintermediatebetweenmuscle-typeandcytoplasmic-typeactins.Theseresultsstronglysuggestthatthenotochordofadultamphioxusisamechanicalswimmingorgananditsroleisquitedifferentfromtheroleofthevertebrateembryonicnotochord,whichfunctionsasasourceofsignalsrequiredforbodyplanformation.

[学科分类] 生物科学（综合）

[关键词] amphioxus;notochord;EST analysis;muscle genes;actins;notochordal sheath;extracellular matrix;chordate evolution