INS and obesity due to melanocortin 4 receptor deficiency: In the present review, on the basis of the recent progresses in understanding the molecular mechanisms that regulate folliculogenesis in mammals, we highlight and discuss how disturbance of insulin/IGF-dependent signalling and increased ROS level in the ovary typically associated to metabolic disorders such as type II diabetes and obesity can dysregulate the dynamics of the ovary reserve and/or impair the survival and competence of oocytes.