Gonadal cell lineages of the nematode Panagrellus redivivus and implications for evolution by the modification of cell lineage☆

[摘要] Toexplorethenatureofcelllineagemodificationsthathaveoccurredduringevolution,thegonadalcelllineagesofthenematodePanagrellusredivivushavebeendeterminedandcomparedtotheknowngonadallineagesofCaenorhabditiselegans(J.KimbleandD.Hirsh,1979,Develop.Biol.70,396–417).Essentiallyinvariantlineagesgeneratethe143somaticcellsofthemalegonadandatleast326somaticcellsofthefemalegonadofP.redivivus.Thebasicprogramofgonadogenesisisstrikinglysimilaramongbothsexesofbothspecies.Forexample,theearlydivisionpatternsofthesomaticgonadprecursorsZ1andZ4arealmostidentical.Laterdivisionpatternsaremoredivergentand,inafewcases,generatestructuresthatarespeciesspecific.Ingeneral,similarcelltypesareproducedaftersimilarpatternsofcelldivisions.DifferencesamongtheZ1andZ4celllineagesappeartoreflectphylogeneticmodificationsofacommondevelopmentalprogram.Thenatureofthesedifferencessuggeststhattheevolutionofcelllineagesinvolvesfourdistinctclassesofalterations:switchesinthefateofacelltothatnormallyassociatedwithanothercell;reversalsinthepolarityofthelineagegeneratedbyablastcell;alterationsinthenumberofroundsofcelldivision;andan“alteredsegregation”ofdevelopmentalpotential,sothatapotentialnormallyassociatedwithonecellinsteadbecomesassociatedwithitssister.AnumberofcelldeathsoccurduringgonadogenesisinP.redivivus.ThedeathofZ4.pp,acellthatcontrolsthedevelopmentoftheposteriorovaryinC.elegans,probablypreventsthedevelopmentofaposteriorovaryinP.redivivusandhenceisresponsibleforthegrossdifferenceinthemorphologiesofthegonadsoftheP.redivivusfemaleandtheC.eleganshermaphrodite.AsexemplifiedbythedeathofZ4.pp,analterationinthefateofa“regulatorycell”couldfacilitaterapidand/ordiscontinuousevolutionarychange.

[学科分类] 生物科学（综合）