Windowing Chicken Eggs for Developmental Studies

The study of development has been greatly aided by the use of the chick embryo as an experimental model. The ease of accessibility of the embryo has allowed for experiments to map cell fates using several approaches, including chick quail chimeras and focal dye labeling. In addition, it allows for molecular perturbations of several types, including placement of protein-coated beads and introduction of plasmid DNA using in ovo electroporation. These experiments have yielded important data on the development of the central and peripheral nervous systems. For many of these studies, it is necessary to open the eggshell and reclose it without perturbing the embryo's growth. The embryo can be examined at successive developmental stages by re-opening the eggshell. While there are several excellent methods for opening chicken eggs, in this article we demonstrate one method that has been optimized for long survival times. In this method, the egg rests on its side and a small window is cut in the shell. After the experimental procedure, the shell is used to cover the egg for the duration of its development. Clear plastic tape overlying the eggshell protects the embryo and helps retain hydration during the remainder of the incubation period. This method has been used beginning at two days of incubation and has allowed survival through mature embryonic ages.

1. Remove eggs from incubator

1. Maintain at 37°C with relative humidity set above 60%.
2. Remove the eggs; turn eggs 90° so that the large base lies horizontal.

2. Swab eggs to sterilize

1. Saturate a stack of non-sterile gauze with 70% ethanol.
2. Use two to three pieces to swab up to 5 eggs. Discard when the gauze is soiled.

3. Preparing albumen removal site

1. Cut and place a 1" x 1" piece of 3M plastic tape just left of the base to protect the area where the albumin will be drawn out.

4. Removal of albumen

1. U....

This method allows for long survival times following experimental manipulations. For example, dye-labeling studies allowed survival to E10 or later in a fate mapping study (1). In addition, it has been used for in ovo electroporation studies that provide alteration of gene expression levels and required development to proceed to later developmental stages (2-6). This windowing technique can be used in combination with any procedure that requires survival after manipulations to the embryo.

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