Mesenchyme of embryonic reproductive ducts directs process outgrowth of Retzius neurons in the medicinal leech☆

摘要

Inthetwosegmentsofthemedicinalleech(Hirudomedicinalis)thatcontainthemale(segment5)andthefemale(segment6)reproductiveducts,thepairedRetzius(Rz)neuronsaredistinguishedbyseveraluniqueproperties.Forexample,themusclesandglandsofthebodywallaretheprimaryperipheraltargetsofRzneuronsinstandardsegments[Rz(X)],whereasthemusclesandglandsofthereproductiveductsaretheprimaryperipheraltargetsofRzneuronsinthetworeproductivesegments[Rz(5,6)].Inthispaper,weshowthatorganogenesisanddifferentiation,whichgenerateanepithelialtubesurroundedbymesenchymalcells,occurintheembryonicreproductiveductsatapproximatelythetimewhenRzprocessesfirstcontactthesestructures.ThegrowthconesleadingonebranchoftheposterioraxonofRz(5,6)contacttheductmesenchymalcells.Followinginitiationofthiscontact,theseposteriorgrowthconesenlargeandsendoutnumerousfilopodia.Secondarily,growthconesleadingtheanterioraxonofeachRz(5,6)alsomodifytheirshapesandtrajectories.Whenembryonicreproductiveductsweretransplantedintoposterior(nonreproductive)segments,thebranchoftheposteriorRzaxonneartheectopicreproductivetissueproducedenlargedgrowthconesandextendedseveralsecondarybranchesintothemesenchymeoftheectopictissue.Thisresultsuggeststhatthereproductivemesenchymeisattractiveto,andcanmodifythegrowthof,allRzneurons.ThebehaviorofRz(5,6)growthconessuggeststhatthereproductivemesenchymecellsprovideguidancecuesthatcontrolthelocationinwhichRzaxonselaboratetheirperipheralarborizationandformsynapses,andthatthemesenchymemayalsostimulatetheproductionofadenselybranchedarbor.