Axis determination in the avian embryo

Publisher Summary This chapter describes the anatomical and morphological aspects of the early stages of chick development and a new consensus terminology. The dynamics of cell populations and the cell interactions during the early developmental stages are fundamental to the analysis of the gradual processes of axis determination in the chick embryo. Hence, the gradual steps that determine the bilateral symmetry of the embryo are examined, as will the sequential processes that establish the posterior–anterior axis of the embryo. This chapter mainly describes the developmental potential of the marginal zone and the role of the hypoblast in the formation of the primitive streak. In addition, issues concerning the molecular and cellular basis of mesoderm induction and formation in the chick embryo are discussed in this chapter. The formation of the axis in the avian embryo is a complex integrative and sequential process that produces highly organized axial structure from the fertilized egg. The unfertilized avian egg shows a distinct radial symmetry and is polarized along its animal-vegetal axis that was determined during oogenesis. The determination of the axis in the avian embryo is a multistep process at the molecular and cellular levels. The unfertilized avian egg shows a distinct radial symmetry. After the egg is fertilized, the bilateral symmetry of the embryo is determined, by the formation of the polarized area pellucid, during the intrauterine stages.