The Second Meiosis Occurs in Cytochalasin D-Treated Eggs of Corbicula leana Even Though It Is Not Observed in Control Androgenetic Eggs because the Maternal Chromosomes and Centrosomes Are Extruded at First Meiosis

[摘要] ThehermaphroditicfreshwaterclamCorbiculaleanareproducesbyandrogenesis.Inthecontrol(androgeneticdevelopment),allmaternalchromosomesandmaternalcentrosomesatthemeioticpoleswereextrudedasthetwofirstpolarbodies,andsubsequently,secondmeiosisdidnotoccur.But,inC.leanaeggstreatedwithcytochalasinD(CD)toinhibitpolarbodyextrusion,thesecondmeiosisoccurred.Atmetaphase-I,thespindleshowedthetypicalbipolarstructureandtwospheroidcentrosomeswerelocatedatitspoles.Allthematernalchromosomesweredividedatanaphase-I,buttheywerenotextrudedaspolarbodiesduetotheeffectsofCD.Aftercompletionoffirstmeiosis,thematernalcentrosomessplitintofour.Atthesecondmeiosis,twinortetrapolarspindleswereformedandtwogroupsofmaternalchromosomesdividedintofoursetsofchromosomes.Afterthesecondmeiosis,thespindledisassociatedandthefourmaternalcentrosomesdisappeared.Fourgroupsofmaternalchromosomestransformedintothefourfemalepronuclei.Maleandfemalepronucleibecamemetaphasechromosomesofthefirstmitosis.ThepresentstudyclearlyindicatesthattypicalmeiosissystemsstillproceedinandrogenetictriploidC.leana.Weconcludethattheandrogeneticformmayhavearisenfromthemeioticform.

[学科分类] 生物科学（综合）

[关键词] bivalvia;androgenesis;cytochalasin D;second meiosis;tubulin;centrosomes;spindle;pronuclei