What we can learn from the bovine embryo and mouse models to enable in vitro gametogenesis in cattle

The development of in vitro gametogenesis (IVG) in the mouse opened up unforeseen possibilities for assisted reproduction. The development of this technology to be used in cattle production could accelerate the rate of genetic selection by dramatically reducing the generation interval, while decreasing the environmental impact of livestock production as the need to grow animals in the process of genetic selection would be reduced or even eliminated. Although several steps of the process of IVG such as in vitro oocyte maturation and fertilization, and embryo production are already routinely performed in cattle, other steps of the system such as in vitro follicle and oocyte development are still rudimentary. The stable derivation of bovine pluripotent stem cells is the starting point without which IVG cannot be realized. However, producing a primordial germ cell and taking this cell through oogenesis and folliculogenesis in a dish will require a more detailed understanding of the milestones that need to be accomplished in vivo before they can be recapitulated in vitro. In particular, understanding the regulatory circuitry of germ cell specification in the embryo, the timing and events related to development of the germ cell program, and the factors necessary to make a competent egg, will need to be uncovered. Here, we review the process of IVG and provide a brief description of the current advances and bottlenecks related to in vitro oogenesis and folliculogenesis in cattle. Finally, we provide a brief comparison between mice and cows in this regard.