"Vesicle transport and cytoplasmic streaming in the pollen tube tip"
The rapid elongation of the pollen tube in seed plants cannot occur without the transport of sufficient cell wall and membrane material to the growing apex. The movement of this material, delivered via exocytic secretory vesicles, can be categorised under two regimes: 'long distance' movement in the shank (via active transport along actin ﬁlaments), and 'short distance' movement in the apex (where vesicles diffuse and advect freely). Many current models of vesicle transport focus on diffusion in the apical region alone, neglecting advective eﬀects as well as the resulting distribution proﬁle in the pollen tube shank. Using the method of regularised Stokeslets with an adjustment made for axisymmetry, we produce a complete advective velocity proﬁle for cytosolic ﬂow in the tube based on the drag induced by the active transport of vesicles along actin. We use this to calculate exocytic and endocytic vesicle motion in the tube, incorporating vesicle uptake and deposition at the wall, and generating insight into pollen tube growth dynamics.
"A new model for the HPA axis explains dysregulation of stress hormones on the timescale of weeks"
Stress activates a complex network of hormones known as the Hypothalamic-Pituitary-Adrenal (HPA) axis. The HPA axis is dysregulated in chronic stress and psychiatric disorders, but the origin of this dysregulation is unclear and cannot be explained by current HPA models. To address this, we developed a new mathematical model for the HPA axis that incorporates changes in the total functional mass of the HPA hormone-secreting glands. The mass changes are caused by the HPA hormones which act as growth factors for the glands in the axis. We find that the HPA axis shows the property of dynamical compensation, where gland masses adjust over weeks to buffer variation in physiological parameters. These mass changes explain the experimental findings on dysregulation of cortisol and ACTH dynamics in alcoholism, anorexia and postpartum. Dysregulation occurs for a wide range of parameters, and is exacerbated by impaired glucocorticoid receptor (GR) feedback, providing an explanation for the implication of GR in mood disorders. These findings suggest that gland-mass dynamics may play an important role in the pathophysiology of stress-related disorders.
"Modeling early hepatitis D virus kinetics in transgenic-hNTCP mice"
The hepatitis delta virus (HDV) is a dependent virus of hepatitis B virus that uses hepatitis B surface antigen to create its envelope and achieve secretion. HDV infection is the most severe form of chronic viral hepatitis. Currently, no therapies have been approved that can cure delta hepatitis. Understanding of early HDV-host dynamics post infection is lacking. I will present early serum HDV kinetics in transgenic mice expressing human NTCP (tg-hNTCP), the receptor for hepatitis B virus and HDV, and non-tg control mice after inoculation and provide insights into HDV-host interplay using mathematical modeling.