19.4: Chick and Quail

Another classic system in which to vertebrate development has been studied extensively is the chick embryo. Fertilization occurs internally; the egg is laid after ~24 hours and hatches ~21 days later. It is possible to open the egg without disturbing embryonic development, which allows for tissue removal (extirpation) and transplantation studies. Fertilized chicken eggs are relatively inexpensive and the tools involved are fairly standard.^[616] Another important factor is that it is possible to transplant tissues between quail (Coturnix coturnix japonica) and chicken (Gallus gallus) embryos. While these birds and their eggs are of different sizes, their developmental rates are similar. Importantly, cells from transplant and host can be distinguished based on chromatin organization: in both embryonic and adult quail cells heterochromatin is condensed into a small number (1 to 3) of aggregates in the central region of the nucleus. These can be visualized using histological staining (Feulgen-Rossenbeck) reaction (→). In more modern studies, it has been possible to transplant chick cells transgenic for GFP expression; such chimeric embryos often develop normally and may hatch.

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