Dynamic Changes to the Inositol 1,4,5-Trisphosphate and Ryanodine Receptors during Maturation of Bovine Oocytes

Abstract

The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) and ryanodine receptor (RyR) have been identified as two ligand-gated calcium channels which play a critical role in mediating calcium release in many different types of cells and tissues. The physiological significance of the two receptors in regulation of intracellular calcium during meiotic maturation and fertilization in the bovine oocyte was evaluated. Metabolic labeling of bovine oocytes by Met-Cys 35S during early and late maturation was followed by immunoprecipitation of both RyR and IP3R using specific antibodies against these two receptors. Results indicate that IP3R is translated throughout the maturation period; in contrast, RyR is only translated during the late maturation period of bovine oocytes. In addition, the experiments reported here investigate the temporal and spatial relationships between these calcium channels and the endoplasmic reticulum (ER) and cortical granules (CG). Immunocytochemistry, fluorescence staining and confocal microscopy were applied at four oocyte developmental stages: the germinal vesicleintact (GV-intact), metaphase I (MI) and metaphase II (MII) stages of maturation and the fertilized egg at 6 h post insemination (hpi). Although oocytes demonstrated some differences in staining patterns and localization, both receptor types showed apparent dynamic changes during meiotic maturation and dramatic decreases in signals after insemination. These results indicate the changes in the number and distribution of IP3R and RyR may account for the increased intracellular calcium responsiveness at fertilization. The IP3R appears to associate with the ER at the sub-vitelline membrane cortex in bovine oocytes. In addition, RyR appears to associate with the CG. In conclusion, although these two receptors may have different functional roles in regulation of calcium release during meiotic maturation and fertilization, it appears that both IP3R and RyR contribute to the significant increase of intracellular calcium during fertilization and activation in the bovine oocyte.

Relocalization of STIM1 in mouse oocytes at fertilization: early involvement of store-operated calcium entry

“…First, we show that endogenous STIM1 is expressed in oocytes, and that this expression is remarkably dependent on the maturation stage, being upregulated after GVBD. This developmentally upregulated profile of protein expression is similar to that found for other Ca 2C transport systems that have been shown to be involved in the generation of calcium waves at fertilization in oocytes, such as InsP 3 R and RyR (He et al 1997, Parrington et al 1998, Wang et al 2005. Therefore, the SOCE, a STIM1-dependent pathway, could be considered to be a probable contributor in Ca 2C signaling in oocytes.…”

Role of Store-Operated Calcium Entry During Meiotic Progression and Fertilization of Mammalian Oocytes

“…However, ER clusters disappear at the completion of meiosis II, and the ER aggregates around the mitotic spindle in the first mitotic division . In a similar manner, InsP 3 R clustering decreases after fertilization, and these receptors diffuse into the central region of the bovine oocyte (Wang et al, 2005). In a similar manner, InsP 3 R clustering decreases after fertilization, and these receptors diffuse into the central region of the bovine oocyte (Wang et al, 2005).…”

“…In GV oocytes, InsP 3 R1 is found throughout the cytoplasm, but enriched in small clusters (<1mm) located around the cortex (Fissore et al, 1999;Mehlmann et al, 1996). RyRs are found mainly in the cortex of MI and MII oocytes and are associated to cortical granules in bovine oocytes from the MI stage through fertilization, suggesting that RyRs may play a key role in cortical granule release (Wang et al, 2005;Yue et al, 1998). As stated for InsP 3 Rs, RyRs show a very weak and diffuse distribution in GV oocytes, whereas the expression is greater in MI and MII oocytes.…”

Discovery of putative oocyte quality markers by comparative ExacTag proteomics

“…Other notable oocyte proteins with a connection to UPP have been identified in our ExacTag ™ trial: RyR, upregulated in the high-quality oocytes, is involved in calcium signaling during fertilization and has been shown to be translated only during the final stages of bovine oocyte maturation [45]. The number of RyR receptors is thought to be regulated by UPP in skeletal muscle [46].…”