Regulation of Meiosis during Mammalian Spermatogenesis: The A-Type Cyclins and Their Associated Cyclin-Dependent Kinases Are Differentially Expressed in the Germ-Cell Lineage ☆

摘要

TobegintoexaminethefunctionoftheA-typecyclinsduringmeiosisinthemale,wehaveexaminedthedevelopmentalandcellulardistributionofthecyclinA1andcyclinA2proteins,aswellastheircandidatecyclin-dependentkinasepartners,Cdk1andCdk2,inthespermatogeniclineage.ImmunohistochemicallocalizationrevealedthatcyclinA1ispresentonlyinmalegermcellsjustpriortoorduringthefirst,butnotthesecond,meioticdivision.Bycontrast,cyclinA2wasexpressedinspermatogoniaandwasmostabundantinpreleptotenespermatocytes,cellswhichwillenterthemeioticpathway.ImmunohistochemicaldetectionofCdk1wasmostapparentinearlypachytenespermatocytes,whilestainingintensitydiminishedindiploteneandmeioticallydividingspermatocytes,thecellsinwhichcyclinA1expressionwasstrongest.Cdk2washighlyexpressedinallspermatocytes.Notably,incellsundergoingthemeioticreductiondivisions,Cdk2appearedtolocalizespecificallytothechromatin.Thiswasnotthecaseforspermatogoniaundergoingmitoticdivisions.Inthetestis,cyclinA1hasbeenshowntobindbothCdk1andCdk2butweshowherethatcyclinA2bindsonlyCdk2.TheseresultsindicatethattheA-typecyclinsandtheirassociatedkinaseshavedifferentfunctionsintheinitiationandpassageofmalegermcellsthroughmeiosis./p/div