One consequence of fertilization in mammals is an increased resistance of the zona pellucida (ZP) to proteases and various chemical reagents. This phenomenon has been called 'zona pellucida hardening' (ZPH), and it is generally accepted that it
is
caused by the secretory products of cortical granules released by the egg at fertilization. ZP of mouse oocytes maturing in vitro in a chemically defined medium becomes progressively more resistant to solubilization by chymotrypsin ("spontaneous"
ZP
hardening).
In the present study, it was aimed to find the specificity of spontaneous ZPH in relation to its possible relevance to the cortical reaction and he physiological block to polyspermy.
When a maturation inhibitors, cAMP analog (dbcAMP) an phosphodiesterase inhibitor (IBMX) was added to culture medium, it prevent spontaneous ZPH of mouse oocyte during in vitro culture. Thus spontaneous ZPH requires GVBD, since it is prevented by
those
agents, which inhibit GVBD in vitro.
However, culture for 3 hours in the presence of PMA (10ng/ml), a protein kinase C activator, resulted in ZPH without GVBD, thus suggesting that ZPH may be regulated independently apart from the event of GVBD.
Pretreatment of mouse oocyte with FBS result in partially inhibitory effect on subsequent spontaneous ZPH.
Induction of GVBD in vivo had a inhibitory effect on the spontaneous ZPH, but subsequent spontaneous ZPH.
Induction of GVBD in vivo had a inhinbitory effect on the spontaneous ZPH, but had no inhibitory effect on PMA-induced ZPH.
Treatment with a microfilament formation blocker (cytochalasin-B) at 1μg/ml concentration, resulted in the excellent inhibitory effect on spontaneous ZPH. However cytochalasin-B did not inhibit PMA-induced ZPH. Thus this suggesting that
spontaneuse ZPH
had a different mechanism from PMA-induced ZPH.
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