Development and Control of Tissue Separation at Gastrulation in Xenopus

[摘要] DuringXenopusgastrulation,theinternalizingmesendodermalcellmassisbroughtintocontactwiththemultilayeredblastocoelroof.Thetwotissuesdonotfuse,butremainseparatedbythecleftofBrachet.Thismaintenanceofastableinterfaceisapreconditionforthemovementofthetwotissuespasteachother.Weshowthatseparationbehavior,i.e.,thepropertyofinternalizedcellstoremainonthesurfaceoftheblastocoelroofsubstratum,spreadsbeforeandduringgastrulationfromthevegetalendodermintotheanteriorandeventuallytheposteriormesoderm,roughlyinparalleltointernalizationmovement.Correspondingly,theblastocoelroofdevelopsdifferentialrepulsionbehavior,i.e.,theabilitytospecificallyrepellcellsshowingseparationbehavior.Fromtheeffectsofoverexpressingwild-typeordominantnegativeXB/UorEP/Ccadherinsweconcludethatseparationbehaviormayrequiremodulationofcadherinfunction.Further,weshowthatthepaired-classhomeodomaintranscriptionfactorsMix.1andgscareinvolvedinthecontrolofseparationbehaviorintheanteriormesoderm.Wepresentevidencethatinthisfunction,Mix.1andgscmaycooperatetorepresstranscription.