Association of mammalian SMC1 and SMC3 proteins with meiotic chromosomes and synaptonemal complexes

In somatic cells, the heterodimeric Structural Maintenance of Chromosomes ( SMC) proteins are involved in chromosome condensation and gene dosage compe nsation (SMC2 and 4), and sister chromatid cohesion and DNA recombination ( SMC1 and 3). We report here evidence for an involvement of mammalian SMC1 a nd SMC3 proteins in meiosis, Immunofluorescence analysis of testis sections showed intense chromatin association in meiotic prophase cells, weaker sta ining in round spermatids and absence of the SMC proteins in elongated sper matids. In spermatocyte nuclei spreads, the SMC1 and SMC3 proteins localize in a beaded structure along the axial elements of synaptonemal complexes o f pachytene and diplotene chromosomes. Both SMC proteins are present in rat spermatocytes and enriched in preparations of synaptonemal complexes. Seve ral independent experimental approaches revealed interactions of the SMC pr oteins with synaptonemal complex-specific proteins SCP2 and SCP3, These res ults suggest a model for the arrangement of SMC proteins in mammalian meiot ic chromatin.