Metabolic behaviour and cleavage capacity in the amphibian egg.

During the winter season the full grown Bufo arenarum oocyte shows the metabolic behaviour characteristic of differentiated tissues of the same species. Due to seasonal variations, during the amplexus period, it acquires the metabolic behaviour of the segmenting egg. Short-time-induced ovulations (5-6 h) determine germinal vesicle breakdown immediately before the expulsion of the oocyte, without modifying the ovarian metabolism of the same. The incidence of the operative type of metabolism upon their capacity to cleave after insemination and needle pricking, has been studied in coelomic oocytes, which have attained nuclear maturation and have not experienced oviducal secretion effects. The results obtained indicate that the segmenting capacity of the egg is attained only when, through biochemical modifications, the oocyte acquires the metabolic behaviour characterizing embryonic cells. It is postulated that the metabolic changes observed in the oocyte constitue a fundamental aspect of cytoplasmic maturation.