Gonad establishment during asexual reproduction in the annelid Pristina leidyi

摘要

Animalsthatcanreproducebybothasexualagameticreproductionandsexualreproductionmusttransmitorre-establishtheirgermlinepost-embryonically.Althoughsuchadualreproductivemodehasevolvedrepeatedlyamonganimals,howasexuallyproducedindividualsestablishtheirgermlineremainspoorlyunderstoodinmostgroups.WeinvestigatedgermlinedevelopmentintheannelidemPristinaleidyi/em,aspeciesthattypicallyreproducesasexuallybyparatomicfission,intercalatinganewtailandheadinthemiddleofthebodyfollowedbysplitting.Wefoundthatinfissioningindividuals,gonadsoccurinanteriorsegmentsintheanterior-mostindividualaswellasinnewheadsformingwithinfissionzones.Homologsofthegermline/multipotencygenesempiwi/em,emvasa/em,andemnanos/emareexpressedinthegonads,aswellasinproliferativetissuesincludingtheposteriorgrowthzone,fissionzone,andregenerationblastema.Infissioninganimals,certaincellsontheventralnervecordexpressahomologofempiwi/em,areabundantnearfissionzones,andsometimesmakecontactwithgonads.Suchcellsaretypicallyundetectableneartheblastemaandposteriorgrowthzone.Time-lapseimagingprovidesdirectevidencethatcellsontheventralnervecordmigratepreferentiallytowardsfissionzones.Ourfindingsindicatethatgonadsformroutinelyinfissioningindividuals,thatapopulationofempiwi/em-positivecellsontheventralnervecordisassociatedwithfissionandgonads,andthatcellsresemblingtheseempiwi/em-positivecellsmigratealongtheventralnervecord.Wesuggestthattheempiwi/em-positiveventralcellsaregermcellsthattransmitthegermlineacrossasexuallyproducedindividualsviamigrationalongtheventralnervecord./p/div