Experimental studies on a mutant gene (e) preventing the differentiation of eye and normal hypothalamus primordia in the axolotl☆☆☆

[摘要] Thephenotypeofaxolotls(Ambystomamexicanum)homozygousforthemutantgenee(“eyeless”)isdifferentfromnormalinthat(1)noopticvesiclesdevelopineeembryos,(2)eelarvaefromposthatchingonwardaredarkerthannormalwhitelarvae,and(3)fullygrowneeanimalsaresterile.Experimentsreportedhereshowthateyelessnessineeembryosresultsfromadirecteffectofthegeneonpresumptiveforebrainectoderm;notonthemesodermthatinducestheectodermtoformeyes.Homotopicgraftsofnormalpresumptiveectodermoneeblastulahostsdifferentiatedcompleteeyes,butreciprocallygraftedembryoswerealwayseyeless.Similarly,graftsofeithereeornormalpresumptiveprechordalmesodermintonormalhostsgavenormaleyes,butinthemutanthostsnoeyesdeveloped.Thustheegeneaffectsonlytheectodermalcomponentoftheinductivesystemforeyeformation.Geneticallyeyeless(pigmented)cells,wheninterspersedpriortogastrulationamonggeneticallyeyed(albino)cellsintheeyepreprimordium,areinducedtoformclonesofpigmentedretinalepitheliuminthealbinohosteye.Thesterilityofeelarvaeappearsalsotobeduetoadirecteffectoftheegeneontheectodermal(neuralplate)primordiumofthehypothalamus.Graftsofnormalcellswhichincludedthehypothalamic,butnottheopticoranteriorpituitaryprimordia,alwaysrestoredfertilitytoeerecipients.Themutantpigmentationphenotypewasdemonstratedtobeaconsequenceofeyelessnessand,therefore,anindirecteffectofthegene.Thepigmentpatternofnormalembryosfromwhichbothopticvesicleswereremovedresemblesthatofthemutants.Inaddition,implantationofasinglefull-sized,functionaleyewasabletorestorethenormalpigmentation,butnotfertility,toeerecipients.

[学科分类] 生物科学（综合）