Actin filaments, stereocilia, and hair cells of the bird cochlea: III. The development and differentiation of hair cells and stereocilia☆

摘要

Thecochleaeofchickembryosof8daysofincubationuntilhatching(21days)wereexaminedbyscanningelectronmicroscopy.Unlikewhatonewouldexpectfromtheliterature,thetotalnumberofhaircellspercochlea(10,405?±529)isalreadydeterminedandvisibleina10-dayembryoandthegrowthofthecochleaisaresultofthegrowthinsizeandsurfaceareaofthehaircells.Wealsofindthatthehaircellsdifferentiatesimultaneouslythroughoutthecochleaandhavefollowedthedifferentiationofindividualhaircellsthroughoutdevelopment.Duringdevelopmentwefindthatthetotalnumber,hexagonalpacking,andorientationofthestereociliaineachhaircellisdeterminedearlyandaccurately(9-to10-dayembryos).Thestereociliathenbegintoelongateinallthecellsofthecochleaatapproximately0.5??m/day.ByDay12thetalleststereociliaineachcellare1.5a€“1.8??mlong,thematurelengthforcellsattheproximalendofthecochlea.Atthispointallstereociliaceaseelongating,butthosealongtheinferioredgegraduallyincreaseinwidthfrom0.11??mtomaximally0.19??min17-dayembryos.Whenthestereociliaontheinferioredgereachtheirmaturewidth,wideningceasesandtheelongationofstereociliainthedistalhaircellsbeginsagain.Whenthesestereociliahaveattainedtheirmaturelengths,theystopgrowing.Thuselongationandwideningofstereociliaareseparatedintime.Duringthisperiod,11to13days,theshapeofthetuftsattheproximalendofthecochleachanges.Thisoccursbecausestereociliainthefrontofeachtuftareabsorbedwhileothersatthesidesappeardenovo.Thisrearrangementconvertsacircularbundleofstereociliatoarectangularbundle.