Exo Ovo Culture of Avian Embryos

Exo ovo culture of avian embryos is a technique for long-term culturing of embryos outside of their own shell and shell membranes. The problem of how to gain access to the avian embryo while allowing it to grow normally has been the subject of many studies (1 ). Avian embryos are subjected to various environmental conditions in the course of normal development. For example, in the chick embryo, in the first day, development takes place in the oviduct where egg formation is completed by deposition of thick and thin albumen, uterine fluid, chalaza, inner and outer shell membranes, and shell around the yolk; for the next 21 d, the enveloping layers act as a buffer between the embryo and the egg’s environment (2 ). Current technologies now permit the culture of avian embryos from the single-cell stage (which is normally in the oviduct) through hatching. We can take out just fertilized ovum, inject DNA and mRNA, and culture until hatching. The choice of culture method depends on the age of the embryo at the start of the experiment. In contrast to shell windowing techniques, the exo ovo culture allows easy access to the developing embryos and is thus useful for analysis of the developmental process of embryos and embryo manipulation. Injections and microsurgical operations can be made into a specific portion of the embryo, including transplantation of undifferentiated tissues and primordia and microsurgery of limb buds. Avian embryos, especially chick and quail embryos, have been widely used for studies of developmental and molecular biology. Fertile and embryonated eggs are accessible all over the world as well as throughout all seasons of the year.