Differences in spindle association of the mitotic checkpoint protein Mad2 in mammalian spermatogenesis and oogenesis

We have investigated expression and subcellular localization of the spindle checkpoint protein Mad2 during rat and mouse spermatogenesis and in supero vulated mouse oocytes. Our immunofluorescence studies demonstrate substanti al differences in the localization patterns of kinetochore-associated Mad2 in these meiotic systems compared with previous studies of mitosis. In addi tion, the association of Mad2 with second-division-metaphase kinetochores d iffered significantly in male versus female meiosis. In spermatogenesis, Ma d2 remained at most kinetochores throughout the entire first meiotic divisi on and was lost only at metaphase of the second meiotic division. This resu lt indicates that loss of kinetochore-associated Mad2 is not essential for the metaphase-to-anaphase transition during the first meiotic division. Dis ruption of the male meiotic spindles with the microtubule depolymerizing ag ent nocodazole resulted in the appearance of Mad2 at nearly all kinetochore s. In contrast, the microtubule stabilizer taxol induced the loss of Mad2 f rom the majority of the first-division-metaphase kinetochores in which it w as normally present in untreated cells. In contrast to the situation in spe rmatogenesis, Mad2 persisted at the kinetochores of normal, second-division oocytes at metaphase. These findings suggest that the role of the kinetoch ore in signaling in the spindle checkpoint may differ markedly between mamm alian mitosis and meiosis, between the two meiotic divisions, and between m ale and female meiosis. (C) 2000 Academic Press.