Transformations of sperm nuclei incorporated into sea urchin (Arbacia punctulata) embryos at different stages of the cell cycle☆

摘要

Inordertotestthehypothesisthatregulatorsofmalepronucleardevelopmentmayhaveamoregeneralrole,sharingsomerelationtofactorsinvolvedwiththecellcycle,Arbaciazygotesand2-to8-cellstageembryoswereinseminatedduringdifferentphasesofthecellcycleandexaminedbylightandelectronmicroscopy.Differencesinthedevelopmentandmorphologyoffertilizationconesandspermasterswereobservedinembryosinseminatedduringdifferentstagesofthecellcycle.Extremelylargefertilizationcones,approximatelyfourtimesthelengthofthosefoundinfertilizedeggs,formedinembryosinseminatedduringmetaphasetotelophase.Spermastersdevelopedonlyinembryosinseminatedduringprophasetoanaphase.Thesevariationsarebelievedtoreflectchangesinthestatusofthecortexandcytoskeletalsystemoftheembryo.Althoughspermnucleiunderwentmorphologicalchangessubsequenttoincorporation,ingeneral,theyfailedtodevelopintomalepronuclei.Therewasaconsistentcorrelationinspermnucleartransformationsandthecellcyclewhichwasexpressedintwopatternsofmorphogenesis:(1)spermnucleiincorporatedintoembryosjustpriortoprophaseandattelophasefailed,forthemostpart,todisperseandtransformedintoaggregationsofchromatingranulesapproximately40nmindiameter;and(2)spermnucleiincorporatedintoprometaphase-anaphaseembryosdispersedandthencondensedintochromatinmasses,morphologicallysimilartochromosomesoftheembryo.Evidenceisdiscussedwhichindicatesthatfollowingthenormalperiodoffertilizationchangesoccurinthezygote,renderingitunabletofullysupportthetransformationofspermnucleiintomalepronuclei.