Biochemical changes in the cytoplasm of bovine oocytes during the in vitro maturation process: a Raman microscopy study.

The sequence and chronology of the main biochemical changes occurring in the cytoplasm of bovine oocytes during the in vitro maturation process were tracked by Raman microscopy applied to cells previously subjected to enzymatic digestion of the zona pellucida. Specific spectral markers for proteins, lipids and carbohydrates were used to evaluate the developmental status of the ooplasm at four different times. Spectral changes revealed that lipid accumulation was dominant during the first six hours of culture while protein content reached the average levels characteristic of mature oocytes within the last four hours of the maturation process. A time-dependent decrease in carbohydrates was also observed. Finally, the carbohydrate-to-protein (P 1037 /P 1002 ) ratio proved to be sensitive enough to determine the cytoplasmic maturation state of bovine oocytes and promises to be useful in future research aimed at optimizing culture conditions through the promotion of protein accumulation in the ooplasm.