Epidermal fine structure in embryonic chicken skin during atypical differentiation induced by vitamin a in culture

[摘要] Thechangesinepidermalfinestructurethataccompany(a)keratin-likeformationinembryonicmetatarsalskingrowninnormalmedium,(b)mucousmetaplasiainducedbyexcessofvitaminA,and(c)cytodifferentiationinskintransferredfromvitaminAtonormalmedium,havebeenanalyzed.Epidermaldifferentiationincontrolexplantsdiffersincertainrespectsfromthatofnormalembryonicskininovo.Thereisaprecociouslossofperidermleadingtoanincreaseincytoplasmicsapinthesuperficialstratum.Thebasalcellsbecomemoredenselypackedwithfinefilamentswhicharethoughttorepresentanearlystageintheformationofkeratin.Thefilamentscoalesceintheupperlayerstoformtonofibrilswhichareconfinedtotheperipheryofthecytoplasm.Thetonofibrilscondenseattheuppersurfaceoftheskintoformaloosestratumcorneum,butthedegreeofmacromolecularorientationislessthanthatinovo.WhenculturesareexposedtoexcessvitaminAthebasalandlowerspinosumcellsbecomedisorientedandintercellularlacunaeincrease.Filamentsdisappearalmostcompletelyinthebasalcells,andkeratinizationisarrested.Allcellsshowagenerallackofdensity,andanapparentincreaseincytoplasmicsap.Mitochondriaenlargewithacorrespondingincreaseinmitochondrialsap,butthereisnodisruptionoftheinternalorganization;thiseffectisgreatestinthebasalcells.TheGolgizonesshownoobviouschange.Mucousglobulesdonotappearuntilaboutthesixthday,butmucoussecretionbeginsmuchearlier.MicrovilliareformedattheoutersurfaceoftheepidermisasanimmediateresponsetoexcessvitaminAeveninthosecellswhich,althoughpreventedfromformingkeratin,haveadvancedtoofaralongtheirnormaldevelopmentalpathwaytoundergomucousmetaplasia.InvitaminA-treatedexplantstransferredtonormalmedium,within2daysthegeneraldensityofthecellsincreasesgreatlyandthemitochondriaappearnormal.Filamentsrapidlydevelopinthecytoplasmofthedeepercellularstrata,thusindicatingareversionofthecellstotheirnormalfunction;henceinthegerminativecellsaparticulartypeoforganizationlastsonlyaslongastheenvironmentthatevokesit.Mucousglobulesdevelopinthecentralcells,thecontentsofeachglobulebeingfirstlocatedinthecytoplasmicsap,andthenenclosedbyamembrane;thesecellsmoveupwardtothesuperficiallayersandformtypicalgobletcells,theglobulesbeinginterconnected.Thedifferentiationofgobletcellsisgreatlyenhancedforseveraldays,showingthatinthesecellstheresponsetovitaminAcontinuesinspiteofachangedenvironment.Thereisnogrossextrusionofglobularmaterialfromthecells,anobservationsuggestingthatthesecretionmustbeoffairlylowmolecularweight.Theappearanceofbothmucousglobulesandfilamentsinthesamecellinthemiddlestrataindicatesthatundercertainenvironmentalconditionscellsbecomedifferentiatedforthesimultaneousperformanceoftwoquitedifferentspecializedfunctions.

[学科分类] 生物科学（综合）