Germ cell-specific nucleocytoplasmic shuttling protein, tesmin, responsive to heavy metal stress in mouse testes.

Tesmin 60, a novel testis-specific gene, has been identified to have homology in plant and animal species, sharing a pair of cysteine-rich regions reported to be similar to metallothionein. The functional implications for these homologs, however, are not fully understood. Two plant homologs are involved in regulating transcription or floral development. cDNA was transfected in COS-1 cells using GFP as a tag. The tesmin-GFP chimeric protein revealed its cytoplasmic localization, which is inconsistent with findings for the plant homologs. We hypothesized that the putative regulatory protein tesmin could be under the regulation of the nucleocytoplasmic shuttling by the effect of metal stress. Immunocytochemistry of male germ cells revealed that tesmin mainly locates in the cytoplasm at stages I-VIII of pachytene spermatocytes, while it temporarily translocates into the nucleus in the late pachytene or diplotene stages X-XII under normal conditions. This is one of a few examples of a germ cell-specific protein that undergoes temporal and spatial regulation through the G2/M transition in meiosis. This nucleocytoplasmic translocation of tesmin is also stress-responsive. Administration of cadmium causes loss of temporal regulation in spermatocytes. This observation suggests the testis is more sensitive to stresses than other organs. This is necessary to maintain genetic integrity.