Early stimulation of phospholipid methylation in Xenopus oocytes by progesterone

Progesterone induced a transient increase in the incorporation of [³H]methyl groups into phospholipids of Xenopus oocytes followed by a rise in ⁴⁵Ca²⁺ uptake. Phospholipid methylation reached a maximum as early as 15 s after progesterone treatment and returned to basal level within 2 min. Steroids inactive in promoting oocyte maturation were less effective in affecting phospholipid methylation. Methyltransferase inhibitors, 3-deaza-SIBA, SIBA, and Sinefungin, inhibited progesterone-activated stimulation of phospholipid methylation, calcium uptake and meiotic maturation. Phospholipid methylation is the earliest detectable biochemical event occurring in oocytes after exposure to progesterone followed by calcium influx and leading to germinal vesicle dissolution.