Endocrine dynamics modelling on the hypothalamic-pituitary-gonadal axis of the aquatic lower vertebrates

The endocrine signalling pathways of the lower vertebrates in the aquatic environments (e.g., fish and amphibians) comprise multiscale biochemical networks ranging from the subcellular transcriptomes, cell and tissue-specific metabolisms, and hormone-mediated inter-organ communications. The entire signalling circuitry thus typically demonstrates a dynamic complexity controlled by the physiological mechanisms such as cardiovascular circulation and neurosecretory regulations. The primary cross-talk paths involved in this circuitry can be effectively reduced to the serial multi-organ system linking the brain, ovary or testis, and liver, which is often called the hypothalamic-pituitary-gonadal (HPG) axis.In this presentation, we develop a general theoretical framework as a model for the signalling pathway network that regulates the HPG axis of the aquatic lower vertebrates. A linear system of ordinary differential equations was constructed to represent the metabolic networking structure where the uni- and bi-directional signalling flows and homeostatic feedback loops were coupled together. The model was designed to predict the dynamic behaviours of hormone syntheses in the HPG axis by simulating the environmentally relevant steroidogenic perturbations. Using this mechanistic model, it was shown that some potential scenarios of ecological risks could be quantitatively predicted in terms of the reproductive toxicology.