Defective cell cohesivity expressed late in the development of a Dictyostelium discoideum mutant☆

[摘要] MutantJC-5,derivedfromstrainFR-17whichisitselfamutantofDictyosteliumdiscoideum,exhibitslateindevelopmentatemperature-sensitivemorphogeneticdefectassociatedwiththelossofEDTA-resistantcellcohesivity.Atthepermissivetemperature(22°C)themorphogeneticsequencefollowedbyJC-5isinqualityandtiminglikethatoftheparentstrain.Attherestrictivetemperature(27°C)themutantinitiallyformsnormalaggregatesbutstartingat11–12hrtheserapidlydispersetoasmoothlawnofdissociatedcellswhichneverthelesscompletetheirdifferentiationintosporesandstalkcellsonschedule.Aggregatesshiftedfrom22to27°Cat11hrdispersepromptlyandcompletely,andthoseshiftedevenaslateas13–14hrregressmarkedly.Aggregatesshiftedfrom27to22°Cat11hrcontinuenormalmorphogenesisuninterruptedandthoseshifted1–2hrlateraftersignificantdispersionhasoccurredcanberescued.Theseeventsobservedonsolidsubstratumarepreciselycorrelatedwiththemaintenance,loss,orrecoveryofEDTA-resistantcohesivityassayedinshakensuspension.Pastthecritical11-hrstage(butnotbefore)mutantcellscanbemadetolosecohesivityevenatthepermissivetemperaturebyexposuretocycloheximideand,havinglostitattherestrictivetemperature,canregaincohesivityatthepermissivetemperatureonlyintheabsenceoftheinhibitor.Incontrast,cycloheximideleavesthecohesivityoftheparentstrainunaffectedatanystage.Ghostsderivedfromcohesivecellsexhibitnormalcohesivitywhenassayedatthepermissiveorrestrictivetemperature.Ghostsderivedfromnoncohesivecellsarenoncohesiveateithertemperature.Theseresultsindicatethatthedefectliesintheinabilityofmutantcellslateindevelopmentattherestrictivetemperaturetomaintainormobilizeacriticallevelofaplasmamembrane-associatedmoietyrequiredforcohesion.Ifpresent,however,itcanfunctionateithertemperature.Expressionorrepairofthecohesivedefectwasnotaccompaniedbysignificantchangesinthelevelsofcontactsite-Aglycoprotein,assayedbyelectrophoreticmobilityandlabelingwith[14C]acetate,orofcarbohydratebindingprotein(“discoidin”),assayedbyhemagglutinatingactivity.Correlativechangeswereobservedinseveralproteinscapableofbindingwith125I-labeledwheatgermagglutininorconcanavalinAbutthereisnoindicationasyetthatanyofthembearsacausativerelationtothedefect.

[学科分类] 生物科学（综合）