Spatiotemporal pattern of calmodulin and [Ca2+]i is related to resumption of meiosis in mouse oocytes.

During meiotic maturation, mammalian oocytes undergo a series of morphological and physiological changes that prepare them for fertilization. Calcium-initiated signaling is thought to trigger these processes. In this study, we examine the spatio-temporal pattern of calcium and calmodulin (CaM), its downstream receptor, in order to investigate their association with meiotic maturation. Intracellular free calcium and activated CaM levels were measured using the fluorescent probes Calcium Green-1 and TA-CaM, respectively. The distribution patterns were examined using confocal microscopy. Both calcium and activated CaM showed a dynamic spatiotemporal distribution during meiotic maturation. After release from IBMX buffer, calcium was found to periodically translocate from the perinuclear region to the germinal vesicle (GV) in 90 s intervals. After 90 min, calcium stopped oscillating and became concentrated within the GV. After a further 60 min, the GV broke down and calcium dispersed into the ooplasm, but calcium levels were slightly lower here than in the original nuclear region. Activated CaM also showed a dynamic patterning process similar to calcium. Taking the data from calcium chelation and CaM inhibition together, our results suggest that the dynamic distribution patterns of calcium and activated CaM are crucial for oocyte maturation.

[Study on the role of calcium signal during mature resumption of isolated mouse germinal vesicles in a cell free system].

A cell-free system including HeLa cell lysate of synchronized metaphase or G2-phase and isolated germinal vesicles (GV) from mouse oocytes was used to study the role of calcium and its downstream mediator during mature resumption. The isolated GVs could resume meiotic maturation in the lysate prepared from M phase HeLa cell, which marked by chromatin condensation. And this process was not affected by calcium chelating agent. But calcium in lysate from G2 phase cells was critical to meiotic maturation. Only in mid-G2 phase cell lysate (released from nocodazole for about 20-23h) chromatin condensation could be induced by calcium. Calcium had no effect on the cell lysate prepared from earlier (18-20h) and later (24h) G2 phase cells. Further studies showed that down stream mediator CaM and CaMKII might also involove in this process. Inhibition the function of CaM and CaMKII could block GVBD and first polar body extrusion of DOs cultured in vitro. The target of calcium signal might be MPF because MPF was existed from mid-G2 phase to metaphase and the tyrosine phosphorylation level of Cdc2 subunit was significantly dephosphorylated in M phase. Our results further confirmed that the resumption of meiosis maturation was promoted in a calcium/CaM depended pathway.