Archive for the 'Cortical Reaction' Category

16 Dec

Segregation of the Pathways Leading to Cortical Reaction: DISCUSSION(6)

hese results are in agreement with previous studies showing that in the cascade of events for induction of the CR, PKC activation by TPA acts downstream to Ca2+ (Xenopus ), and that PKC activators induce CG exocytosis, facilitating ZP modification and the block to polyspermy (mouse ). At fertilization, the egg is activated either by […]

15 Dec

Segregation of the Pathways Leading to Cortical Reaction: DISCUSSION(5)

Thus, a maximal CR in the majority of the eggs could be obtained in the present study only when [Ca2+]; levels increased by > 400 nM, triggered either by ionomycin or by OAG. A similar increase of [Ca2′ ], was observed at the initial calcium transient in rat eggs activated by sperm at fertilization. TPA […]

14 Dec

Segregation of the Pathways Leading to Cortical Reaction: DISCUSSION(4)

When Ca2+ was chelated to 150200 nM only, 14% of the eggs resumed meiosis, but half still underwent a CR. Only when the Ca2+ transient was chelated to 95 nM or lower were both aspects of activation inhibited to less than 10%. In addition, our results demonstrate that while different magnitudes of the single Ca2+ […]

13 Dec

Segregation of the Pathways Leading to Cortical Reaction: DISCUSSION(3)

In the present study, a distinct variability in the sensitivity of eggs to Ca2+ levels was demonstrated. While iono-mycin induced a Ca2+ transient of 340 nM that was adequate to cause activation in only about half (57%) of the eggs, 434 nM induced activation in the majority (87%). Under these conditions, eggs were induced to […]

12 Dec

Segregation of the Pathways Leading to Cortical Reaction: DISCUSSION(2)

The phorbol ester TPA has been previously shown to be an activator of PKC, similar to the physiological activator diaclyglycerol (DAG). Accordingly, OAG, the synthetic DAG, induced the CR in the same manner as that of TPA. In contrast to TPA, which induced only partial cell cycle resumption, a complete cell cycle resumption (including a true […]

11 Dec

Segregation of the Pathways Leading to Cortical Reaction: DISCUSSION(1)

In the present study, we demonstrated a segregation between the pathway leading to the CR and that of cell cycle resumption, during early events of egg activation. Our results illustrate that resumption of the cell cycle is Ca2+-dependent but is PKC-independent. Treatment of Mil eggs with increasing concentrations of ionomycin raised the fraction of eggs […]

10 Dec

Segregation of the Pathways Leading to Cortical Reaction: RESULTS(5)

Loading eggs with BAPTA-AM resulted in a concentration-dependent inhibition of both the CR and resumption of meiosis (Fig. 7A). However, inhibition of meiotic resumption was more sensitive to Ca2+ levels than was inhibition of the CR. When 0.5 |xM BAPTA was used, only 14% of the eggs resumed meiosis, whereas more than 50% underwent a […]

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