[Cyclooxygenase in ooplasm is essential for early embryonal differentiation but not for successful fertilization in the mouse].

It has been known that inhibition of prostaglandin (PG) synthesis interferes with successful implantation. The present study dealt with the chronology in cyclooxygenase (COX) expression and the effects of inhibition in mouse oocytes in the perifertilization period. COX protein was detected in both oocytes and fertilized eggs whereas the mRNA was not found by a high sensitivity RT-PCR only in blastocysts. Oocytes which were sham operated or micro-injected with preabsorbed anti-COX monoclonal antibody (hPES01) or non-immune IgG were fertilized and developed to two-cell embryos, whereas hPES01 injected oocytes were fertilized but failed to differentiate (p < 0.05 chi 2-analysis). This inhibitory effect on early embryonal development of COX inhibition was also seen in indomethacin pre-cultured oocytes which were successfully fertilized but failed to develop further. We concluded that the COX gene which is one of the immediate early genes is not transcribed in the perifertilization period but the enzyme which remains in the cytoplasm and the presence of intact COX before fertilization are essential for early embryonal differentiation.