The Chick Embryo as a Model System for Analyzing Mechanisms of Development

The chick embryo provides an excellent model system for studying the development of higher vertebrates wherein growth accompanies morphogenesis. (Note: virtually all information given here for the chick embryo is applicable to the quail embryo, and much of it is applicable to embryos of other avians including domesticated and wild species.) There are many advantages to working with chick embryos. Chicken eggs are available year-round, they are inexpensive, and they can be purchased in any specified quantity (no excess or shortfall). If eggs are acquired and used within a week, unincubated eggs can be stored in any cool place, obviating the need for a special storage facility. Chicken eggs can be incubated to any stage of interest, simplifying experimental design and allowing the investigator to coordinate his or her schedule with the need to have embryos at the desired developmental stage for a particular experiment. At the time the egg is laid, the avian embryo consists of a flat, two-layered blastoderm that lies on the surface of the yolk and, therefore, is readily accessible. Subsequent development occurs with incubation at 38�C and is rapid. Within 2 to 3 d of laying, chick embryos gastrulate, neurulate, and fold into three-dimensional (3-D) animals with beating hearts, somites, and complex nervous systems. Such rapid development is an advantage for experimental design and timely data collection. During this period of early development when so much is occurring, chick embryos can be easily removed from the shell for culture, or they can be cultured in ovo . Embryos are semitransparent, making viewing of internal tissues possible under the microscope, and they are of sufficient size to make several types of micromanipulation practical at these early stages.