The development of bioluminescence in the ctenophore Mnemiopsis leidyi☆

[摘要] ThephotocytesofthectenophoreMnemiopsishaveadiscontinuousdistributionalongtheradialcanalbetweenthesiteswherethecombplateciliacellsarelocatedonthesideofthecanalwhichcontainsthetestes.Theyareseparatedfromthelumenofthecanalbyapopulationofgastriccells.Cytologicallythesecellsarecharacterizedbyacondensednucleusandcytoplasmwhichstainslightlywithbasophilicdyes.Theabilityofthectenophoreembryotoproducelightappearsatthedevelopmentalstagewhenthecombplateciliafirstbegintogrowout.Atthisstagefourlight-producingareasarepresent;eachareacorrespondstoonequadrantoftheadultanimal.Atthesitesoflightproduction,apopulationofcellscanbeidentifiedthathavesomeofthecytologicalpropertiesofthephotocytesoftheadultanimal.Within8–10hrafterlightproductionbeginsthereisa10-foldincreaseintheamountoflightproducedbyanembryoandacytologicalmaturationofitsphotocytes;duringthistimeperiodthereisnoincreaseinphotocytenumber.Ataboutthetimetheembryobeginstofeed,eachlight-producingregionsplitsintotworegions,eachofwhichcorrespondstoaradialcanal.Duringtheprocessofembryogenesisthephotocytecelllineageisfirstsegregatedfromnon-photocytesatthedifferentialdivisionwhichgivesthe8-cellstageembryo.TheMmacromerelineagegoesontoformphotocytes,buttheEmacromerelineagedoesnot.TheMmacromeresformamicromereattheaboralpoleoftheembryoateachofthenexttwocleavages;duringthesecleavagesthepotentialforphotocytedifferentiationcontinuestosegregatewiththeMmacromeres.Duringthedivisionwhichgivesthe64-cellstagetheMmacromeresdivideequally;thepotentialforphotocytedifferentiationsegregateswiththeMmacromeresnearesttheoral-aboralaxis.Mmacromereswhichareisolatedfromtheembryoatthe8-,16-,or32-cellstageofdevelopmentwillcontinuetocleaveasthoughtheywerepartofanormalembryoanddifferentiatetoformphotocytes.Theeventsthatareresponsibleforthedifferentialdivisionduringtheformationofthe8-cellstageembryohavebeenstudiedbycentrifugingeggstoproducefragmentsofdifferentcytoplasmiccomposition.Eggfragmentswhichcontainonlycorticalcytoplasmdifferentiatecombplateciliacells,butdonotproducephotocytes.Corticalfragmentswithasmallamountofyolkdifferentiatecombplateciliacellsandphotocytes.BoththeMandEmacromeresfromcorticalfragmentswithnoyolkproducecombplatecilia.OnlyMmacromerescontainingyolkformphotocytes;ifanMmacromereformsphotocytesitdoesnotformcombplatecilia.

[学科分类] 生物科学（综合）