The loss of phenotypic traits by differentiated cells: IV. Changes in polysaccharides produced by dividing chondrocytes☆

[摘要] Thebehaviorof10-day,embryonic,vertebralchondrocyteswasexaminedinthreedifferentinvitrosituations.Chondrocytesculturedinintactcartilagessynthesizedasulfatedpolysaccharidewhichwasindistinguishablefromchondroitinsulfate.NonetDNAsynthesiswasdetectedinsuchcartilages.Whenliberatedfromtheirmatrixandculturedaspellets,chondrocytescontinuedtosynthesizechondroitinsulfateandremainedanessentiallypostmitoticpopulation.Identicalcellsculturedasmonodispersepopulationsonplasmaclots,ceasedsynthesizingchondroitinsulfateandbegantosynthesizeDNAandothermoleculesnecessaryforcelldivision.ConcomitantlywiththeinitiationofDNAsynthesis,anunsulfatedpolysaccharideappearedinthesystem.Thispolysaccharidewasnotsynthesizedbysimilarcellsinintactcartilagesorinpellets.Whentheinitiallymonodisperseculturesbecame“crowded,”netDNAsynthesisceasedandthecellsbeganmakingsulfatedpolysaccharides.Unsulfatedpolysaccharidecontinuedtobesynthesizedin“crowded”cultures.Cellsfromliverandmusclewereculturedunderthesameconditionsaswerechondrocytes.Thesepopulationssynthesizedbothunsulfatedandsulfatedpolysaccharidesindispersedandconfluentcultures.Itisconcludedthat(1)chondroitinsulfatesynthesisandDNAsynthesisappeartobemutuallyexclusiveprocesses,(2)intimatecellassociationisoptimalforthemaintenanceofthecartilagephenotype,(3)lackofassociationwillinducereplicationtogetherwithlossoftheabilitytosynthesizechondroitinsulfate,and(4)manycelltypesmayreacttoaninvitroexperiencebydividingandsynthesizingbothunsulfatedandsulfatedpolysaccharides.

[学科分类] 生物科学（综合）