The selective activation of only a few of several hundred thousands primordial follicles to mature into an oocyte is a riddle which has not at all been solved. In a paper in Current Biology Chang and colleagues from Gothenburg, Sweden, place this decision onto the microenvironment of the primary cell, especially the few primordial follicular granulosa cells surrounding each primordial follicle. They show that mTORC1 activation and Kit ligand signalling are required steps in the activation, mTORC1 defective animals never develop primary follicles, the primordial follicular cells die.

They do not answer the question which follicle is to grow, but placing the decision to the surrounding is a paradigma change and will focus the experiments and the discussion away from the oocyte precursors which cells seems more or less “only” to react to the surroundings. Given that this cell is dormant and needs strong signals to be activated this is comprehensible. At least we know now who the cascade of events is initiated.

Whether this has consequences for in vitro fertilization we will see. The question why so few follicles are activated during the reproductive life of women is not answered by this article.

Nice and recommended!