The utilization of an inhibitor of spermidine and spermine synthesis as a tool for the study of the determination of cavitation in the preimplantation mouse embryo.
The inhibition of spermidine and spermine synthesis by methylglyoxal-Bis(guanylhydrazone) (MeGAG) at concentrations of 5, 10 and 20 microM, induces a reversible metabolic quiescence of mouse embryos, cultured in vitro from the 2-cell stage, at an average of 10.2, 8.5 and 6.9 cell stages respectively. In contrast, the inhibition of putrescine synthesis by alpha-methylornithine (alpha-MeOrn) at concentrations up to 10 mM fails to inhibit blastocyst formation, as shown previously. Complete reversibility of this induced arrest of development is observed for treatments up to 31 h with MeGAG at 10 microM. In agreement with the biological clock theory of Smith & MacLaren's hypothesis, the delay in cavitation is proportional to the length of treatment. However, the average cell numbers of the 'delayed nascent blastocysts' of all treated embryos (21.8--24.2) are consistently lower than that of control embryos (33.6) irrespective of the duration of treatment. It seems therefore that under some experimental conditions, DNA and chromosome replication on the one hand and cytoplasmic maturation on the other may be desynchronized. This suggests a role for a cytoplasmic factor in the induction of cavitation.