Development of highly efficient homologous recombination system using mouse recombination genes and establishment of mouse strains with gene engineered

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The mouse Rad51 gene is a mammalian homologue of the Escherichia coli recA and yeast RAD51 genes, both of which are involved in homologous recombination and DNA repair in mitosis and meiosis. The expression of mouse Rad51 mRNA was examined in cell-cycle synchronized mouse m5S cells. The Rad51 transcript was observed from late G1 phase through to M phase. During the period of late G1-S-G2 phase, the RAD51 proteins were exclusively observed in nuclei. Activation of T cell and B cell proliferation in spleen by mitogens induced the expression of Rad51 mRNA.By immunohistochemical analyzes, the mouse RAD51 protein was detected in proliferating cells ; spermatogonia in testis, immature T cells in thymus, germinal center cells of the secondary lymphatic nodules of spleen and intestine, follicle cells in ovary and epithelial cells in uterus and intestine. It was also expressed in spermatocytes during the early and mid prophase of meiosis and in resting oocytes before maturation. Thus mouse Rad51 expression is closely related to the state of cell proliferation and is presumably involved in DNA repair coupled with DNA replication as well as meiotic DNA recombination in spermatocytes.