Sulphydryl reagent iodoacetamide inhibits progression of meiosis and sperm transformation in mouse oocytes fertilisedin vitro

The effect of iodoacetamide (IA), a sulphydryl blocking agent, on fertilisation in the mouse was examined by transferring zona-free oocytes into IA (500 microM)-containing medium at various times after insemination. When inseminated oocytes were transferred into IA medium 10 min after insemination, the oocyte chromosomes remained aggregated in one or two masses and the sperm nucleus failed to decondense. When oocytes were transferred during the second meiosis, oocyte meiosis was more or less arrested. The sperm nucleus decondensed but remained blocked at an early stage of decondensation. These observations suggest that thiol groups in the oocyte's cytoplasm and perhaps microtubules of the meiotic spindle play crucial roles in the completion of meiosis and the transformation of sperm nucleus into pronucleus.