Neurotrophin signaling in oocyte survival and developmental competence: a paradigm for cellular toti-potency

While not fulfilling the criterion of a "stem cell" in being capable of self-renewal, mature and fertilized oocytes are the original "toti-potent" cells, whose capacity for expansion and differentiation can only be approximated by stem cells of embryonic or adult origin in vitro. As such, the mechanisms by which oocytes acquire and manifest competence to support embryo development is of fundamental interest to efforts to control and re-specify somatic cell fate and toti-potency. This is underscored by the unparalleled capacity of oocyte cytoplasm to successfully re-specify the genetic program of animal development following cell nuclear replacement (i.e., cloning). Thus, the knowledge gained by understanding the acquisition of oocyte developmental competence could ultimately facilitate the creation of adult stem cells in vitro from terminally differentiated cells, ex ovo. In this paper, we review the concept of oocyte developmental competence, and focus on our own research and that of others implicating a role for neurotrophins in this process, and that of oocyte cell survival. Lastly we propose a role for neurotrophin signalling in embryo stem cell survival.