Dynamics of steroid-induced oocyte maturation in three amphibian species: Mathematical modeling and simulation

Oocyte maturation in vertebrates involves morphological, biochemical, and functional changes through which meiosis, previously arrested in Profase I, is resumed. Within these changes, germinal vesicle breakdown (GVBD) constitutes morphological evidence of the resumption of the cellular cycle. Sex steroids (progestins and androgens) play a key role in oocyte maturation and are considered inducers of this process. The aims of this study were to analyze the effect of sex steroids on the oocyte maturation of amphibians and to model and simulate the dynamics of this process through the experimental data obtained. The oocytes of sexually mature females of Scinax fuscovarius, Pleurodema borellii, and Physalaemus biligonigerus were treated with different concentrations (0.001-1 µM) of sex steroids progesterone (P ₄ ) and testosterone (T) for 24 hr. Dose- and time-response curves were performed with the results achieved. Sex steroids induced oocyte maturation in a dose-dependent manner in all three species. The dose at which the highest maturation percentage was found was 1 μM. No significant differences were observed between GVBD percentages of P ₄ and T. However, time-response curves show that oocytes responded earlier and achieved higher GVBD percentages when treated with P ₄ . Gompertz mathematical model was proposed in this study to simulate GVBD dynamics. This model properly fits the corresponding experimental data and allows the analysis of the behavior of oocyte maturation in amphibians and the quantification of parameters with biological meaning that are indicative of sex steroids efficiency in this process.