Chapter 1 Operations on Primitive Streak Stage Avian Embryos

This chapter presents the basic techniques necessary for transplantation of cells between regions of the primitive streak stage embryo. It describes transplantation of Hensen's node between quail and chick embryos as a prototype example and present variations of this technique for obtaining other tissues for grafting and guidelines for homotopic or heterotopic grafting. In amniotes (reptiles, birds, and mammals), gastrulation occurs through a midline structure, the primitive streak. At the tip of the primitive streak lies the amniote organizer, Hensen's node. The acquisition of different fates is largely reliant on inductive processes, by which some cells emit signals that influence the fate of their neighbors. The mesoderm, endoderm, and neural plate are all thought to arise from the epiblast as a result of such inductive interactions. To study these events, it is essential to manipulate cells, either to map their normal fates in the embryo, or to challenge their developmental potential by placing cells in a new environment where they may be exposed to different signals, or to test the inducing properties of groups of cells by placing them adjacent to other putative responding tissues. This requires the embryo to be amenable to transplantation and culture to stages after these processes have taken place. The avian embryo lends itself perfectly to manipulations that at the time of laying, it is a large, flat, and translucent disc that can be cultured easily to early organogenesis stages outside the egg.