Regulation of the G2/M phase of the cell cycle by sperm associated antigen 8 (SPAG8) protein.

Sperm associated antigen 8 (SPAG8), a testis-specific protein produced during male germ cell differentiation, was isolated from a human testis expression library using antibodies found in the serum obtained from an infertile woman. It was found to have a close functional relationship with microtubules. In this study, we generated a stably expressing SPAG8 CHO-K1 cell line. Immunofluorescence confocal microscopy showed that SPAG8 was concentrated at the microtubule-organizing center (MTOC) during prophase. As the cells progressed into metaphase, it co-localized with alpha-tubulin on the spindle. In anaphase, it was detected on both astral microtubules and mid-zone. Following cytokinesis, SPAG8 resumed its localization on the MTOC. Meanwhile, flow cytometry analysis found that SPAG8 prolonged the G2/M phase of CHO-K1 cells stably expressing SPAG8. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that SPAG8 inhibited the proliferation of the stable cells. SPAG8 might be involved in the regulation of cell cycle by changing the phosphorylation level of Tyr15 on cdc2. These results suggest that SPAG8 might play a role in cell division during spermatogenesis. (c) 2009 John Wiley & Sons, Ltd.