The initiation of melanogenesis in the chick retinal pigment epithelium☆

[摘要] Observationshavebeenmadeonchickpigmentretinalepitheliumbetween2and5daysofdevelopment.2-Thiouracilhasbeendemonstratedtobeaneffectiveagentformeasuringtherateofmelaninsynthesis.Using[3H]thymidineandcolcimid,wehavefoundthatthecellsundergoamarkedwithdrawalfromthecellcyclebetween3and3.5daysofincubationinovo,indicatingthatamajorityofthepopulationissynchronized.Thiswithdrawalisfollowed,approximately24hrlater,byarapidriseinmelaninsynthesisfromthebasallevelwhichfirstappearsatapproximately3days.5-Bromodeoxyuridine(BUdR)hasbeenusedtodeterminethetimeatwhichmelaninsynthesisisinitiated.WhenBUdRisadministeredasearlyas2daysinovo,itisincapableofblockingtheappearanceofbasallevelsofmelanineventhoughthecellsdivideatleastthreetimesinthepresenceofthisthymidineanalog.However,BUdRiscapableofdelayingtherapidriseintherateofmelaninsynthesisfirstobservedat4.5days.Thisdelayhasbeenfoundtocorrelate,using[3H]BUdR,withadelayinthewithdrawalofthecellsfromthedivisioncycle.Inpursuingtheideaofacorrelationbetweenwithdrawalandtherapidincreaseofmelaninformation,5-fluorodeoxyuridine(FUdR)wasused.HistologicalandbiochemicalevidencesuggeststhatthosecellswhichhavebeenpreventedfromdividingbyFUdRincreasetheirrateofmelaninsynthesistothehighlevelofthepostmitoticcontrolcellsdescribedabove.Therefore,itseemsthat(1),inlightofworkdonebyothers,theinitialdecisiontomakemelaninismadepriorto2daysinovo,and(2)themechanismbywhichcellsshifttheirsyntheticcapabilitiestohighlevelsofmelaninproductioniswithdrawalmediated.

[学科分类] 生物科学（综合）