Development of Dorsal–Ventral Polarity in the Optic Vesicle and Its Presumptive Role in Eye Morphogenesis As Shown by Embryonic Transplantation and in Ovo Explant Culturing

摘要

Dorsalandventralspecificationintheearlyopticvesicleappearstoplayacrucialroleintheproperdevelopmentoftheeye.Inthepresentstudy,weperformedembryonictransplantationandorganculturingofthechickopticvesicleinordertoinvestigatehowthedorsala€“ventral(D-V)polarityisestablishedintheopticvesicleandwhatrolethispolarityplaysinpropereyedevelopment.Theleftopticvesiclewascutandtransplantedinverselyintherighteyecavityofhostchickembryos.ThismethodensuredthattheD-Vpolaritywasreversedwhiletheanteroposterioraxisremainednormal.Theresultsshowedthatthelocationofthechoroidfissurewasalteredfromthenormal(ventral)toectopicpositionsastheembryonicstageoftransplantationprogressedfrom6to18somites.Atthesametime,theshapeoftheopticvesicleandtheexpressionpatternsofPax2andTbx5,markergenesforventralanddorsalregionsoftheopticvesicle,respectively,changedconcomitantlyinasimilarway.Thecrucialperiodwasbetweenthe8-and14-somitestages,andduringthisperiodthepolarityseemedtobegraduallydetermined.InovoexplantculturingoftheopticvesicleshowedthattheD-Vpolarityandchoroidfissureformationwerealreadyspecifiedbythe10-somitestage.TheseresultsindicatethattheD-Vpolarityoftheopticvesicleisestablishedgraduallybetween8-and14-somitestagesundertheinfluenceofsignalsderivedfromthemidlineportionoftheforebrain.Thepresumptivesignal(s)appearedtobetransmittedfromproximaltodistalregionswithintheopticvesicle.Asevereanomalywasobservedinthedevelopmentofopticvesiclesreverselytransplantedaroundthe10-somitestage:theopticcupformationwasdisturbedandsubsequentlytheneuralretinaandpigmentepitheliumdidnotdevelopnormally.WeconcludedthatestablishmentoftheD-Vpolarityintheopticvesicleplaysanessentialroleinthepatterninganddifferentiationoftheneuralretinaandpigmentepithelium.