International Mammalian Genome Society

The 14th International Mouse Genome Conference (2000)

B32. SMC1 and SMC3 Proteins Bind to Meiotic Chromosomes in Mouse Spermatogenesis

Rosalina James1, Kyoko Yokomori2, and Christine M. Disteche1
1University of Washington, Department of Pathology;
University of California, Irvine, Department of Biological Chemistry

The evolutionarily conserved Structural Maintenance of Chromosomes (SMC) proteins 1 and 3 are necessary factors in mitotic sister chromatid cohesion, and are involved in DNA recombination and repair. We previously cloned the mouse X-linked gene (DXHS423) that encodes SMC1. SMC1 and another related protein, SMC3 are shown here to play important roles in meiosis during mouse spermatogenesis. Immunocytochemistry showed that both SMC proteins localized to meiosis-specific structures in a stage dependent manner throughout prophase I, but that the pattern of staining differed between SMC1 and SMC3. Antibody against SMC3 stained the axial core of the aligned chromosomes in cells undergoing zygotene to pachytene transition in mouse spermatocytes. This localization was similar to SMC1 staining pattern in mid-pachytene, except that SMC3 bound along the length of the chromosomes before and after they synapsed, with some of the paired homologues displaying a forked pattern. In contrast, SMC1 associated only with regions where the homologues had paired. The X and Y chromosomes were also bound by anti-SMC3 along the entire axial elements. However, anti-SMC1 signal was restricted to a cluster in the sex body presumably corresponding to the short pseudoautosomal region of homology where the sex chromosomes synapsed. Diplotene cells showed centromeres intensely stained with anti-SMC1, but the antibody did not coat the diplotene chromosomes. Staining with anti-SMC3 bound the axial elements of diplotene structures with chiasmata. In haploid elongating spermatids, both SMC1 and SMC3 co-localized with the spindle pole protein gamma tubulin. These results indicate that SMC3 may play a role in cohesion and condensation of both the sister chromatids and of the homologous pairs, whereas SMC1 may be specifically involved in homologue cohesion of meiotic chromosomes.

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