Chicken as a Developmental Model Gi F Mok, University of East Anglia, Norwich, UK Abdulmajeed F Alrefaei, University of East Anglia, Norwich, UK James McColl, University of East Anglia, Norwich, UK Tim Grocott, University of East Anglia, Norwich, UK Andrea Münsterberg, University of East Anglia, Norwich, UK Introductory article Article Contents • Introduction • Stages of Chick Embryo Development • Manipulation of the Embryo – Classic Experiments • The Molecular Era: Chromosomes and Genome Information • Approaches to Study Gene Function • Transgenic Chickens • Embryo Culture and Live Imaging • The Chicken Model in Biomedical Research • Conclusion th January 2015 The development of a complex organism from a single cell, the fertilised egg, has fascinated peo- ple for centuries. Embryo development is highly reproducible and exquisitely regulated. How is it that all tissues and organs form in the right places and at the right time? How is the development of different organ systems coordinated, so that they all fit together correctly at the end? It is challeng- ing to study development, because many embryos are small or inaccessible. The chick embryo is a popular model system with many experimental advantages, which include classic ‘cut and paste’ experiments and mechanistic gene function analy- ses. The combination of micromanipulations with gain- or loss-of-function is particularly power- ful. The recent development of transgenic lines and advanced imaging techniques ensure that the chicken remains an attractive model system, which will continue to make major contributions to our understanding of molecular and cellular mechanisms controlling developmental processes. Introduction The chick embryo is a classic model to study development in a higher vertebrate, an amniote species. One reason for its popu- larity is the fact that embryos are easily accessible because they eLS subject area: Developmental Biology How to cite: Mok, Gi F; Alrefaei, Abdulmajeed F; McColl, James; Grocott, Tim; and Münsterberg, Andrea (January 2015) Chicken as a Developmental Model. In: eLS. John Wiley & Sons, Ltd: Chichester. DOI: 10.1002/9780470015902.a0021543 develop almost entirely outside the mother. By cutting a ‘win- dow’ into the egg shell, the embryo can be revealed and its growth observed under a low-power microscope (Stern, 2005; Korn and Cramer, 2007). Following manipulations, such as microsurgery or introduction of foreign genetic material, drugs or viruses, the egg can be resealed and re-incubated. When the desired stage of development is reached, embryos can be recovered and har- vested from the egg. The consequences of the manipulation are then investigated using a number of techniques, including cel- lular, molecular and biochemical methods. The chicken genome has been sequenced and molecular and genetic tools are available to interfere with gene function. Through these approaches, work in chick embryos has made important contributions to the eluci- dation of major concepts in vertebrate development, such as the concept of positional information (see also: Positional Informa- tion). Modern molecular tools applied in chick embryos enable us to decipher the mechanisms underlying developmental conditions and malformations, including those observed in human. Stages of Chick Embryo Development To work with chick embryos in the laboratory, it is usually not necessary to house and breed adult animals. Fertilised eggs can be obtained from poultry farms and following delivery, eggs are stored in cooled incubators at 16 ∘ C; for optimal results, eggs should only be stored for 1–2 weeks. When they are needed, eggs are incubated at 37–39 ∘ C for the number of hours or days required to reach the stage of development being studied. This makes working with chick embryos very convenient. The early stages of chick embryo development progress faster when compared to the mouse for example. The mouse is the most commonly used mammalian model species (see also: Mice as Experimental Organisms). However, chicks develop more slowly than the commonly used non-amniote vertebrate model species: the amphibian Xenopus laevis (see also: Xenopus as an Experimental Organism) and the zebraish Danio rerio (see also: Zebraish as an Experimental Organism). Chicks hatch eLS © 2015, John Wiley & Sons, Ltd. www.els.net 1 Online posting date: 27