Ethics of Research involving animals
Studies of animal development
5.12 Developmental biologists often carry out experiments on embryos to determine the cellular and molecular basis of animal development. Parts of an embryo (often chick embryos) are removed to learn about how different tissues develop (see Box 5.5). In some cases, a fragment of tissue is transferred to a new location in the embryo to observe its development. The outcome indicates whether or not the tissue was already irreversibly programmed for development into a particular tissue or organ at the time of transfer. A dye might also be injected into one or more cells, to enable observation of their stages of development. Zebrafish embryos are often used because they are transparent, which is a useful property with regard to monitoring the development of injected cells in the living embryo.
| Box 5.5: Example of research – Developmental studies involving amphibians This is an example of animal research witnessed by some members of the Working Party during a visit to a research laboratory. The main focus of the research was to improve understanding of the processes that determine cell differentiation during the early stages of embryonic development. Researchers used two different species in order to provide comparable information. Amphibian embryos were preferred to mammalian models such as the mouse because amphibians produce a large number of eggs that develop externally to the mother, are of a size which allows experimental reagents to be injected easily, and develop fairly rapidly. The research was undertaken on embryos of the frogs Xenopus laevis and Xenopus tropicalis. In general, the results gained from developmental studies on these frogs are considered to be readily transferable to mammals, including humans, as most of the basic developmental mechanisms have been highly conserved in evolution. The stimulation of egg-laying was the only procedure undertaken in this study that fell under the A(SP)A. Adult female frogs were injected with a hormone that caused them to lay large numbers of eggs within 3-12 hours. This involved a subcutaneous injection just over the dorsal lymph sac. The eggs were fertilised artificially to ensure synchronous development. In order to do so, a male frog was killed by methods referred to in Schedule 1 of the A(SP)A, and its testes was removed and used to fertilise the eggs. Female frogs generate more eggs over a four month rest period and are reused in the procedure described above for the production of new eggs. |