Vascular Remodeling in the Selection of Dominant Follicles

Dominant follicles (DFs) are selected for ovulation out of the population of ovarian growing follicles. The subordinate follicles (SF), which have not been selected during a specific reproductive cycle will eventually degenerate. One of the suggested mechanisms for DF selection relies on the high advantage of their extensive vasculature recruitment. To test this hypothesis, we aimed at developing imaging tools for monitoring changes in follicular vasculature. For tracking changes in permeability and blood volume during DFs selection we used dynamic contract-enhanced MRI. This analysis revealed an elevation in these parameters, which was specifically localized to large follicles. Furthermore, areas with a specific change in these parameters were identified, and their number correlated with the number of ovulating oocytes. Based on optical clearing, we additionally developed the whole organ blood and lymph vessels imaging (WOBLI) method, which allowed the visualization of the entire three-dimensional vascular networks. This method provides a tool for accurate and profound analysis of the structure, connectivity and complexity of the ovarian vasculature under different conditions. In summary, the use of MRI method provided a dynamic functional insight into the vascular properties associated with dominance establishment. Further establishment of the WOBLI method allowed a complete structural analysis of these vessels. A combined use of these two methods will allow the identification of DF and their discrimination from the SF. Having these experimental tools in hand would potentially enable further evaluation of molecular components involved in DFs selection.