Effects of an inhibitor of spermidine and spermine synthesis on the ultrastructure of early mouse embryos

Methylglyoxal-bis (guanylhydrazone) (MG BG) is a potent inhibitor of S-adenosyl-L-methionine decarboxylase, an enzyme involved in the synthesis of the polyamines spermidine and spermine. Its effects on the fine structure of early mouse embryos developing in vitro have been studied. Cleavage is blocked at about the 8-cell stage after culture of the embryos in the presence of 10μM MG BG from the 2-cell stage onwards. The development of the quiescent embryos resumes after transfer into normal medium, but their cavitation is delayed. Moreover, these embryos have about 10 cells less than control embryos at the beginning of cavitation (Alexandre, 1979). The changes, concerning more particularly the lysosomal system, which occur in parallel in control, in embryos treated continuously with MG BG and in embryos transferred to normal medium after about 20 hr of treatment with MG BG, favour the hypothesis of a cytoplasmic 'maturation' proceeding in the absence of nuclear division in quiescent embryos. Embryos treated for 40 hr or more with MG BG show altered nucleoli, less advanced in ultrastructure, often with a reduced granular constituent, probably as the result of an impairment in RNA synthesis and maturation. The changes in the morphology of the mitochondria which occur during normal embryogenesis are not observed in MG BG-treated embryos; the metabolism of these organelles is probably affected by long treatments with the drug.SCOPUS: NotDefined.jFLWNO