Functional differentiation in mouse mammary gland epithelium is attained through DNA synthesis, inconsequent of mitosis

[摘要] Virginmousemammaryglandinexplantculturewilldifferentiateandsynthesizecaseinandα-lactalbuminwheninsulin,hydrocortisone,andprolactin(IFPRL)arepresentintheculturemedium.ExplantswhoseDNAsynthesishasbeenblockeddifferentiatecytologically,mobilizelipid,synthesizeRNA,andincorporate3H-aminoacidsintoproteinstothesameextentasunblockedtissue.Nevertheless,caseinsynthesisasmeasuredbyimmunoprecipitationwithcasein-specificantiserumremainsatthezero-timelevelinblockedexplantswhileunblockedexplantsproducecaseinatfive-toeightfoldgreaterlevels.ElectrophoreticanalysisofimmunoprecipitatedradioactiveproteinsshowedthattheIFPRL-treatedvirgintissuemadeallfoursizeclassesofmousecasein.Immunoperoxidasestudiesofexplantsrevealedthatthenumberofmammaryepithelialcellspositiveforcaseinwas2–8%inblockedand24–31%inunblocked,ingoodagreementwiththeradioimmunoprecipitationresults.ImmunoelectronmicroscopydemonstratedtheaccumulationofcaseinwithinthecisternaeofthegranularendoplasmicreticulumandinGolgivacuolesintheunblockedepithelialcells.Similaraccumulationdidnotoccurinblockedculturesdespitethesecretoryappearanceofthecells.Autoradiographicanalysisofblockedandunblockedexplants,incubatedinthepresenceofIFPRLand[3H]thymidinefor72hr,showedthat53–57%oftheepithelialcellssynthesizedDNAinunblockedexplants,whereasonly2%incorporatedthelabelinthepresenceofcytosinearabinoside.WhenexplantswereincubatedwithIFPRLandvariousconcentrationsofcolchicine,only5–6%oftheepithelialcellswerefoundtoentermitosis.Sincecellduplicationcannotaccountfortheseveralfoldincreaseincasein-producingcellsintheunblockedexplants,theresultssuggestthattherequirementforDNAsynthesisinthissystemmayinvolveeitherpolyploidcellsortheaugmentationofspecificsequencesnecessaryforthefacilitationofterminaldifferentiation.SimilarrequirementsforDNAsynthesiswerenotobservedinmammaryexplantsfrompregnantandprimiparous(butnonpregnant)mice.

[学科分类] 生物科学（综合）