Calcium Release at Fertilization: Artificially Mimicking the Oocyte's Response to Sperm.

Abstract

Abstract. The mechanism of sperm-induced calcium release has been the subject of many studies since the development in the late 1950s of in vitro culture systems that support mammalian fertilization. Despite efforts to elucidate the nature of the signal from the sperm that triggers both the early and late events of oocyte activation, the precise mechanism remains unresolved. Now, with the advent of somatic nuclear transfer technologies, the need to better understand this unique process has been recognised. Nuclear transfer embryos must be induced to commence development artificially because the activating signal from the sperm is absent. The primary activating stimulus is a large increase in the concentration of intracellular-free calcium and numerous physical and chemical treatments have been found to induce calcium changes that initiate the events of oocyte activation. Although live cloned offspring have been produced in a number of species, the overall efficiencies of the nuclear transfer procedures described thus far are unacceptably low and phenotypic anomalies are common. With the aim of improving these efficiencies, researchers are developing artificial activation treatments which induce oocyte responses that mimic those induced by fertilizing sperm. One strategy is to replicate the pattern of calcium change more closely. Another strategy is to couple an activating stimulus with treatments that inhibit maturation (or M-phase) promoting factor (MPF) activity, which regulates meiotic progression in oocytes. This paper reviews what is understood of calcium release at fertilization and describes the treatments that have been used to induce oocyte activation artificially in parthenogenetic and nuclear transfer studies. The relative effectiveness of the strategies employed to mimic the oocyte's response to sperm are discussed. Key words: Oocyte activation, Fertilization, Parthenogenesis, Nuclear transfer (J. Reprod. Dev. 48: 2002) o produce a viable embryo at fertilization, the s p e r m n o t o n l y p r o v i d e s t h e m a l e chromosomal complement, but also the stimulus that initiates development. The mechanism by which the activating signal is transmitted from the sperm to the oocyte is not fully clarified, but it is clear that this signal triggers a large increase in the concentration of intracellular-free calcium. In fertilized sea urchin and Xenopus eggs, the calcium increase takes the form of a propagating wave that originates at the point of sperm attachment and traverses the egg at a velocity of 5 to 10 µm/sec

Morphology of Dromedary Camel Oocytes and their Ability to Spontaneous and Chemical Parthenogenetic Activation

“…Ethanol-induced Ca 2+ elevation would inactivate the existing CSF and MPF, and the subsequent exposure to protein phosophorylation inhibitor (6-DMAP) would prevent renewal of CSF synthesis in the oocyte and support the further development. Grupen et al (2002) recorded that the kinetics of MPF activity following 6-DMAP treatment was similar to that found in inseminated oocytes. However, compared to 6-DMAP, CHX prolonged the first and shortened the third cell cycle, though cytoskeleton activity was initialized, a large proportion of CHX embryos was unable to accomplished first cleavage (Holm et al 2003).…”

“…Ethanol‐induced Ca 2+ elevation would inactivate the existing CSF and MPF, and the subsequent exposure to protein phosophorylation inhibitor (6‐DMAP) would prevent renewal of CSF synthesis in the oocyte and support the further development. Grupen et al. (2002) recorded that the kinetics of MPF activity following 6‐DMAP treatment was similar to that found in inseminated oocytes.…”

“…These authors reported that ethanol activation followed by 6-DMAP gave better results in terms of activation, higher cleavage rate and higher proportion of oocytes developing into morula-blastocysts compared with buffalo oocytes activated in ionomycin followed by 6-DMAP. Ethanol promotes a single intracellular Ca 2+ increase of greater and longer amplitude (Grupen et al 2002), and originates both from extracellular entry of Ca 2+ and mobilization of intracellular stores (Loi et al 1998). Ethanol-induced Ca 2+ elevation would inactivate the existing CSF and MPF, and the subsequent exposure to protein phosophorylation inhibitor (6-DMAP) would prevent renewal of CSF synthesis in the oocyte and support the further development.…”

Control of Spontaneous Activation of Rat Oocytes by Regulating Plasma Membrane Na+/Ca2+ Exchanger Activities

“…While an increase in the intracellular IP3 mediates Ca 2+ release by binding and gating its receptor on the endoplasmic reticulum membrane [22][23][24], DAG may be involved in the regulation of Ca 2+ influx [25,26]. Similarly, it has been shown that parthenogenetic agents activate oocytes also by inducing intracellular Ca 2+ rises [27][28][29][30][31]. Mature rat eggs showed reduced rates of SA when cultured either in calcium-free medium or in calcium-containing medium with L-type calcium channel blocker or IP3 receptor inhibitor [3,32,33].…”

Evaluasi Oosit Kambing Hasil Ivm Sebagai Salah Satu Faktor Penentu Keberhasilan Dalam Aktivasi Partenogenesis

“…Suss dan Madison (1983) dalam Gordon (1994) mengemukakan bahwa dari beberapa oosit yang dimaturasi kirakira sekitar 50% diantaranya menunjukkan adanya PB dengan konfigurasi kromosom pada MII. (Grupen et al, 2002) selanjutnya menurun pada saat sel masuk fase anafase I dan fase telofase I tetapi meningkat kembali pada saat sel masuk dalam fase metafase II sebagaimana halnya seperti yang dialami pada saat metafase I. Sementara itu, cyclin B disintesa dan terakumulasi ketika p34 cdc2 ada dalam sitoplasma yaitu pada saat interfase (Solomon et al, 1990dalam Mayes, 2002) dan terdegradasi oleh ubiquitin-dependent proteolysis. Sebaliknya kadar p34 cdc2 tidak berubah selama meiosis (Choi et al, 1991).…”