Formation of the genital ridges is preceded by a domain of ectopic Sox9-expressing cells in Lepidochelys olivacea

摘要

Bipotentialgonadsrepresentthestructuralframeworkfromwhichalternativemolecularsexdeterminationnetworkshaveevolved.MaintenanceofSox9expressioninSertolicellsisrequiredforthestructuralandfunctionalintegrityofmalegonadsinmammalsandprobablyinmostamniotevertebrates.However,spatialandtemporalpatternsofSox9expressionhavediversifiedalongevolution.Specieswithtemperaturesexdeterminationareaninterestingpredictivemodelsinceoneoftwoalternativedevelopmentaloutcomes,eitherovaryortestisoccursundercontrolledlaboratoryconditions.IntheseaturtleemLepidochelysolivacea/em,Sox9isexpressedinthemedullarycordsofbipotentialgonadswhenincubatedatbothfemale-ormale-promotingtemperature(FTorMT).Sox9isthenturnedoffinpresumptiveovaries,whileitremainsturnedonintestes.Inthecurrentstudy,Sox9wasusedasamarkerofthemedullarycelllineagetoinvestigateifthemedullarycordsoriginatefrommesothelialcellsatthegenitalridgeswhereSox9isupregulated,or,iftheyderivefromacellpopulationspecifiedatanearlierdevelopmentalstage,whichmaintainsSox9expression.Usingimmunofluorescenceandinsituhybridization,embryoswereanalyzedpriorto,duringandaftergonadalsexdetermination.AT-shapeddomain(T-Dom)formedbycytokeratin(CK),N-cadherin(Ncad)andSOX9-expressingcellswasfoundattheupperpartofthehindgutdorsalmesentery.ThearmsoftheT-Domwereextendedtobothsidestowardstheventromedialmesonephricridgebeforethethickeningofthegenitalridges,indicatingthattheycontainedgonadalepithelialcellprecursors.Thereafter,expressionofSox9wasmaintainedinmedullarycordswhileitwasdownregulatedatthesurfaceepitheliumofbipotentialgonadsinbothFTandMT.Thisresultcontrastswithobservationsinmammalsandbirds,inwhichSox9upregulationstartsatalaterstageintheinnercellsunderlyingtheSox9-negativesurfaceepithelium,suggestingthattheestablishmentofaself-regulatorySox9looprequiredforSertolicelldeterminationhasevolved.TheT-shapeddomainattheupperpartofthehindgutdorsalmesenteryfoundinthecurrentstudymayrepresenttheearliestprecursorofthegenitalridges,previouslyunnoticedinamniotevertebrates./p/div