Participation of IP₃R, RyR and L-type Ca²⁺channel in the nuclear maturation ofRhinella arenarumoocytes

Abstract

During meiosis resumption, oocytes undergo a series of nuclear and cytosolic changes that prepare them for fertilization and that are referred to as oocyte maturation. These events are characterized by germinal vesicle breakdown (GVBD), chromatin condensation and spindle formation and, among cytosolic changes, organelle redistribution and maturation of Ca2+-release mechanisms. The progression of the meiotic cell cycle is regulated by M phase/maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAPK). Changes in the levels of intracellular free Ca2+ ion have also been implicated strongly in the triggering of the initiation of the M phase. Ca2+ signals can be generated by Ca2+ release from intracellular Ca2+ stores (endoplasmic reticulum; ER) or by Ca2+ influx from the extracellular space. In this sense, the L-type Ca2+ channel plays an important role in the incorporation of Ca2+ from the extracellular space. Two types of intracellular Ca2+ receptor/channels are known to mediate the intracellular Ca2+ release from the ER lumen. The most abundant, the inositol 1,4,5-trisphosphate receptor (IP3R), and the other Ca2+ channel, the ryanodine receptor (RyR), have also been reported to mediate Ca2+ release in several oocytes. In amphibians, MPF and MAPK play a central role during oocyte maturation, controlling several events. However, no definitive relationships have been identified between Ca2+ and MPF or MAPK. We investigated the participation of Ca2+ in the spontaneous and progesterone-induced nuclear maturation in Rhinella arenarum oocytes and the effect of different pharmacological agents known to produce modifications in the Ca2+ channels. We demonstrated that loading competent and incompetent oocytes with the intracellular calcium chelator BAPTA/AM produced suppression of spontaneous and progesterone-induced GVBD. In our results, the capacity of progesterone to trigger meiosis reinitiation in Rhinella in the presence of L-type Ca2+ channel blockers (nifedipine and lanthane) indicated that spontaneous and progesterone-induced maturation would be independent of extracellular calcium influx, but would be sensitive to intracellular Ca2+ deprivation. As demonstrated by the effect of thimerosal and heparin in Rhinella arenarum, the intracellular increase in Ca2+ during maturation is also mediated mainly by IP3R. In addition, our results using caffeine, an agonist of the RyR, could suggest that Ca2+ release from ryanodine-sensitive stores is not essential for oocyte maturation in Rhinella. The decrease in MPF activity with NaVO3 negatively affected the percentage of thimerosal-induced GVBD. This finding suggests that Ca2+ release through the IP3R could be involved in the signalling pathway that induces MPF activation. However, the inhibition of MAP/ERK kinase (MEK) by PD98128 or P90 by geldanamycin produced a significant decrease in the percentages of GVBD induced by thimerosal. This finding suggests that Ca2+ release per se cannot bypass the inhibition of the MAPK activity.

Expression of G protein estrogen receptor (GPER) on membrane of mouse oocytes during maturation

“…Estrogen-mediated GPERdependent activation of the MAPK Erk1/2 via EGFR transactivation [14,15]. GPER might regulate calcium flux, cAMP and MAPK, leading to oocytes maturation [26,30,31]. The results of the present study showed that the level of GPER expression on oocyte membrane is increased gradually during oocyte maturation, indicating that GPER may act as an oocyte plasma membrane receptor binding to estrogen to influence directly the quality of oocytes maturation.…”

“…It has been shown that estrogen plays a key role in oocytes maturation in mammalian models by inducing a series of cellular signaling including inositol triphosphate (IP3) and ryanodine (Ry)-mediated intracellular free calcium concentration ([Ca 2+ ]i) [23][24][25][26] and calcium signaling [27]. The development of the ability of oocytes to release Ca 2+ in response to the fertilizing spermatozoa is an essential step during oocyte maturation [28].…”

Effect of Wilforine on the Calcium Signaling Pathway in Mythimna separata Walker Myocytes Using the Calcium Imaging Technique

“…Caffeine (100 mM), a known agonist of RyR and an inhibitor of IP 3 R, , was used to further confirm the binding sites of wilforine. The peaks of [Ca 2+ ] i increased to 132.12 ± 2.02% of the initial value after being treated with 100 mM caffeine and could be further increased to 143.07 ± 2.15% after being treated with 100 nM wilforine subsequently (Figure A, Table S4).…”

Transcriptome-wide N6-methyladenine methylation in granulosa cells of women with decreased ovarian reserve

“…It encodes the ryanodine receptor which is one of the components of the intracellular calcium channel. This gene is selectively expressed in ovarian cumulus cells right before ovulation and plays an important role in oocyte maturation and activation [ 82 , 83 ]. In our conjoint study, we found RYR2 was down-regulated and hypo-methylated in older group.…”