Possible role for Ca2+ calmodulin-dependent protein kinase II as an effector of the fertilization Ca2+ signal in mouse oocyte activation

Stein

Proc. Natl. Acad. Sci. U.S.A.

et al. 2009

107

110

Fertilization triggers a rise in intracellular Ca 2+ concentration ([Ca 2+ ] i ) in the egg that initiates a series of events known as egg activation. These events include cortical granule exocytosis that establishes a block to polyspermy, resumption of meiosis, and recruitment of maternal mRNAs into polysomes for translation. Several calcium-dependent proteins, including calcium/calmodulin-dependent protein kinase II (CaMKII), have been implicated in egg activation. However, the precise role of CaMKII in mediating specific events of egg activation and the identity of the isoform(s) present in mouse eggs have not been unequivocally established. Through targeted deletion of the γ isoform of CaMKII, we find that CaMKIIγ is the predominant CaMKII isoform in mouse eggs and that it is essential for egg activation. Although CaMKIIγ −/− eggs exhibit a normal pattern of Ca 2+ oscillations after insemination and undergo cortical granule exocytosis, they fail to resume meiosis or to recruit maternal mRNAs. Surprisingly, we find that the recruitment of maternal mRNAs does not directly depend on CaMKII, but requires elevated [Ca 2+ ] i and metaphase II exit. We conclude that CaMKIIγ specifically controls mouse egg activation by regulating cell cycle resumption.T he transition from a fertilization-competent mammalian egg to a developing embryo entails a sequence of events collectively known as egg activation. Early events of egg activation include modifications of the zona pellucida (ZP) that prevent polyspermy, exit from metaphase II arrest, and completion of meiosis, whereas late events include recruitment of maternal mRNAs into polysomes for translation and formation of male and female pronuclei (1). In all animal species studied to date, a rise in intracellular calcium ([Ca 2+ ] i ) is the universal trigger of all of the events of egg activation (EEA) (2). Release of a spermspecific phospholipase C isoform (PLCζ) likely initiates the inositol 1,4,5-trisphosphate (IP 3 )-mediated increase in [Ca 2+ ] i (3). In mammalian eggs, this increase in [Ca 2+ ] i takes the form of repetitive Ca 2+ transients (oscillations) that last several hours (4, 5). Although Ca 2+ oscillations can induce all of the EEA, individual events require different numbers of [Ca 2+ ] i transients to be initiated and completed, with early events requiring fewer oscillations than late events (6).The pathways that connect the rise in [Ca 2+ ] i to the different EEA have only been partially elucidated. Protein kinases, including calcium/calmodulin-dependent protein kinase II (CaM-KII), and the phosphatase calcineurin have been postulated as integrators of the Ca 2+ signal during egg activation (7-9). However, direct genetic evidence for involvement of these enzymes through loss-of-function studies is lacking, leaving open questions as to whether any single enzyme is essential for all of the EEA or whether these Ca 2+ -dependent events are mediated by different effectors.The CaMKII family of serine/threonine kinases mediates many cellular responses to C...

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The γ isoform of CaM kinase II controls mouse egg activation by regulating cell cycle resumption

Stein

Proc. Natl. Acad. Sci. U.S.A.

et al. 2009

107

110

“…Calmodulin can regulate the activity of many other proteins at fertilization, including calmodulin-dependent kinase II (CaM kinase II). CaM kinase II activity undergoes oscillations following fertilization in mouse eggs (Markoulaki et al, 2003(Markoulaki et al, , 2004, and this activity is important for cortical granule exocytosis and progression through the cell cycle, based on evidence that shows inhibitors of calmodulin or CaM kinase II block both latter processes (Abbott and Ducibella, 2001;Tatone et al, 2002). Notably, CaM kinase II has the ability to regulate NOS function (Michel and Feron, 1997;Schneider et al, 2003).…”

Section: The Role Of Nitric Oxide and Cyclic Adp Ribose During Fertilmentioning

confidence: 99%

Flipping the switch: How a sperm activates the egg at fertilization

Parrington

Davis

Galione

et al. 2007

Developmental Dynamics

Sperm interaction with an egg in animals was first documented 160 years ago in sea urchins by Alphonse Derbè s (1847) when he noted the formation of an "envelope" following the sperm's "approach" to the egg. The "envelope" in sea urchins is an obvious phenotype of fertilization in this animal and over the past 35 years has served to indicate a presence of calcium released from cytoplasmic stores essential to activate the egg. The mechanism of calcium release has been intensely studied because it is a universal regulator of cellular activity, and recently several intersecting pathways of calcium release have been defined. Here we examine these various mechanisms with special emphasis on recent work in eggs of both sea urchins and mice.

“…A role had recently been suggested for proteins, such as CaMKII and calmodulin, in mediating the signal required for the resumption of meiosis (Tatone et al 2002, Markoulaki et al 2003. In a study exploring the role of CaMKII during activation of mouse eggs, Markoulaki et al (2004) demonstrated that CaMKII antagonist inhibits cell-cycle progression in fertilized, but not cycloheximide-treated, eggs.…”

Section: Ionomycinmentioning

confidence: 99%

“…Little is known regarding the cellular pathways by which calcium exerts its signal during egg activation. Recently, a role had been suggested for proteins such as Ca 2þ /calmodulin-dependent protein kinase II (CaMKII) and calmodulin in mediating the signal required for resumption of meiosis (Tatone et al 2002, Markoulaki et al 2003.…”

Section: Introductionmentioning

confidence: 99%

Expression and possible involvement of calpain isoforms in mammalian egg activation

Ben‐Aharon

Haim²,

Shalgi³

et al. 2005

Reproduction

At fertilization in mammals, the spermatozoon triggers a unique signal transduction mechanism within the egg, leading to its activation. It is well accepted that the earliest event observed in all activated eggs is an abrupt rise in intracellular calcium concentrations. However, little is known regarding the downstream proteins that are activated by this rise in calcium. Calpains constitute a family of intracellular calcium-dependent cysteine proteases whose members are expressed widely in a variety of cells. We investigated the expression and possible role of the calpain isoforms m and m throughout egg activation. Both calpains were expressed in the rat egg and localized at the egg cortex as well as in the meiotic spindle. m Calpain translocated to the membrane and to the spindle area during parthenogenetic egg activation and during in vivo fertilization, upon sperm binding to the egg. The cytoskeletal protein a-spectrin (fodrin) was proteolysed by calpain during the egg-activation process, as demonstrated by specific calpain-breakdown products. Following parthenogenetic activation by ionomycin or puromycin, the calpain-selective permeable inhibitor, calpeptin, inhibited the resumption of meiosis and cortical reaction in a dosedependent manner. Calpeptin was also effective in inhibiting in vitro fertilization. These results may imply a correlation between calpain activation and mammalian egg activation at fertilization and a possible role for calpain in the cascade of cellular events leading to resumption of meiosis.