Entry point of an MVC framework

Hi, I have started to develop a simple MVC framework. I have a base controller class which is abstract and all of the controllers are inherited from that. Every controller contains actions represented by methods. (E. g. there is a controller for managing product items in a webshop, and there are seperate actions for create, modify, remove, etc.) There is also a default action (usually an index page), which is used when nothing is requested. But what is the best way to invoke an action? I can't do it with the baseController constructor, becouse parent class can't see inherited classes. And I can't do it with the constructor of the inherited class, becouse this way I would overwrite the parent constructor. And as far as I know, it is not a good practice to call a method outside of the class, becouse the concept of operation of the class should be hidden from the other parts of the application.