Avian scale development: IX. Scale formation by scaleless (scsc) epidermis under the influence of normal scale dermis☆

[摘要] Unlikenormalscutatescaleswhoseouterandinnerepidermalsurfaceselaborateβ(β-keratins)andα(α-keratins)strata,respectively,thescalelessmutant'santeriormetatarsalepidermisremainsflatandelaboratesonlyanαstratum.Reciprocalepidermal-dermalrecombinationsofpresumptivescaletissuesfromnormalandmutantembryoshavedemonstratedthatthescalelessdefectisexpressedonlybytheepidermis.Infact,thescalelessanteriormetatarsalepidermisisunabletoundergoplacodeformation.Morerecently,ithasbeendeterminedthattheabsenceofepidermalplacodemorphogenesisintoadefinitivescaleridgeactuallyresultsintheestablishmentofascaledermiswhichisincapableofinducingtheouterandinnerepidermalsurfacesofscutatescales.Cantheinitialgeneticdefectinthescalelessanteriormetatarsalepidermisbeovercomebyreplacingthedefectivedermiswithanormalscutatescaledermis,i.e.,adermiswithscaleridgesalreadypresent?Or,arethegenesinvolvedintheproductionofaβstratumregulatedbyeventsdirectlyassociatedwithmorphogenesisoftheepidermalplacode?Inthepresentstudy,wecombinedscalelessanteriormetatarsalepidermis(stages36to42)withnormalscutatescaledermis(stage40,41,or42)oldenoughtohaveacquireditsscutatescale-inducingability.After7daysofgrowthaschorioallantoicmembranegrafts,weobservedgrosslyandhistologically,typicalscutatescalesintheserecombinantgrafts.Electronmicroscopicandelectrophoreticanalyseshaveverifiedthattheserecombinantscalesaretruescutatescales.Thescalelessmutation,knowntobeexpressedinitiallybytheanteriormetatarsalepidermis,canbeovercomebyexposingthisepidermistoappropriateinductivecues,i.e.,cuesthatdirectthedifferentiationoftheouterandinnerepidermalsurfacesofthescutatescalesandtheproductionofspecificstructuralproteins.Wehavedeterminedthatthetimebetweenstages38and39isthecriticalperiodduringwhichthenormalscutatescaledermisacquirestheseinductiveabilities.

[学科分类] 生物科学（综合）