The Pem Homeobox Gene Is X-Linked and Exclusively Expressed in Extraembryonic Tissues during Early Murine Development

摘要

WepreviouslyreportedtheisolationofacDNAcloneforahomeobox-containinggenedesignatedemPem/em,shownbyNorthernanalysisofDay7throughDay16mouseembryostobeexpressedinextraembryonictissues.Inthisstudy,Pemgeneexpressionwasfurtherexaminedusingeminsitu/emhybridizationandimmunocytochemistrytodeterminethespatialdistributionofPemtranscriptsandproteininperi-implantationembryosandinembryoidbodies(EBs).LowamountsofPemmRNAweredetectedinundifferentiatedEBs.WhenEBswereinducedtodifferentiate,theoutercelllayerofvisceralorparietalendodermexpressedbothPemmRNAandprotein.Indevelopingembryos,noPemproteinwasdetectableintheuncompactedmorula;12%ofthenucleiincompactedmorulaewerePempositive,while25%oftheblastocysttrophectodermand15%ofinnercellmasscellsexpressedPemprotein.Shortlyafterimplantation,in5.5and6.5d.p.c.embryos,Pemexpressionwaslimitedtoextraembryonictissuesandwaspresentindistalandproximalvisceralendoderm,parietalendoderm,andectoplacentalcone.By7.5-8.5d.p.c.neitherPemRNAnorproteinwasfoundinthedistalsquamousvisceralendoderm,whichsurroundstheembryonicregionoftheeggcylinder,norintheparietalendoderm.Expressionwasretainedintheproximalcolumnarepitheliumofthevisceralendoderm.ProminentPemexpressionwasobservedinthechorion,introphoblast-derivedcellsoftheectoplacentalcone,andinsecondarygiantcells,localizedinthenuclearcompartment.emPem/emwaslocalizedtotheXchromosomeandfoundtobeexpressedincelllineageswhereonlythematernalXchromosomeisactive.ThedataindicateapossibleroleforPeminregulatinggenesinvolvedinthedifferentiationofextraembryonictissues./p/div