Induction of cytoplasmic polarity in heterokaryons of mouse 4-cell-stage blastomeres fused with 8-cell- and 16-cell-stage blastomeres☆

摘要

Cellsurfaceandcytoplasmicpolarityisexhibitedbytheblastomeresofmousepreimplantationembryosfollowingcompactionatthe8-cellstageofcleavage.Ithasbeenhypothesizedthatcytoplasmicpolarityisinitiatedbyplasmamembranefunctionsofpolarblastomeresthatareabsentfromapolarblastomeres.Totestthishypothesistheplasmamembranesofa€?testa€?polarandapolar8-cell-and16-cell-stageblastomereswereinsertedintotheplasmamembraneofa€?carriera€?4-cell-stageblastomeresbypolyethyleneglycol-mediatedfusionofcarrier-testblastomerepairs.Aftera4-hrcultureperiodeachheterokaryonwasscoredforthedistributionoftwomarkerorganellesa€”lipiddropletsandnucleia€”withrespecttotheirproximitytotheplasmamembraneinsertfromthetestblastomere.Plasmamembraneinsertsfrompolartestblastomereswereidentifiedbylabelingtheirapicaldomainswithfluorescentlytagged(succinylated)concanavalinA.Theincidenceofpolarheterokaryons(thoseexhibitingadiscretefluorescentlylabeledareaofplasmamembranecorrespondingtotheapicaldomaininheritedfromthetestblastomere)was5585(69%)and4879(61%)for8-cell-stageand16-cell-stagetestblastomeres,respectively.Inallpolarheterokaryons,bothnucleiweresubjacenttothefluorescentlabel(apicaldomainofapolarplasmamembraneinsert),whilethemajorityoflipiddropletsresidedinthehemisphereoppositethefluorescentlabel.Inall61apolarheterokaryonsexamined(thoselackingadiscretefluorescentlylabeledplasmamembranearea)bothnucleiwerecentrallylocatedandlipiddropletswererandomlydistributed.Theseobservationsareconsistentwiththehypothesisthatcytoplasmicpolaritycanbeinitiatedbypropertiesthatdistinguishtheplasmamembranesofpolarblastomeresfromthoseofapolarblastomeres.