The transplantation of neural tissue provides a means of addressing many questions in developmental neurobiology and regeneration of the nervous system. Although this technique has been used in fish, amphibia, avian, and mammalian species, this chapter will focus on neural transplantation in avia, which has several advantages. The development of the nervous system provides a close parallel to that of mammalian embryos in many of its aspects, and embryos can be accessed at developmental stages impossible in mammals. In addition, avian eggs can be obtained at low cost, and minimal equipment and facilities are required for these types of grafting experiments. Transplantation is possible at both cranial and spinal levels of the neuraxis, but the accessibility of these regions varies with stage. For example, transplantation of brain regions (e.g., ref. 1) is relatively easy at stages in which the neural tube has yet to develop the local expansions of the brain vesicles and has not yet become extensively vascularized, i.e., before E3 in the chick, but becomes more difficult after this time. Stages at which transplantation into the spinal cord (e.g., 2) can be performed depend on the axial level to be investigated owing to the rostro-caudal order of its generation, but transplants into spinal regions remain feasible at later stages.

Examples of the application of neural grafting in chick embryos have been to explore the role of a signaling region by transplanting it to an ectopic site (3) or to investigate the mechanisms of hindbrain segmentation (4). In some experimental paradigms, it is desirable to follow the position and fate of the transplanted tissue in the host environment. For this purpose, chick-quail chimeras have been used extensively to explore a number of developmental questions (see Chapter 22 for detailed discussion). Quail tissues transplanted into a chick host can later be recognized using quail cell-specific or axon-specific

From: Methods in Molecular Biology, Vol. 97: Molecular Embryology: Methods and Protocols Edited by: P. T. Sharpe and I. Mason © Humana Press Inc., Totowa, NJ

antibodies. This allows the fate mapping of cells derived from the grafted tissue or of axon projections arising from the graft. In chick-to-chick transplants, it is also possible to track grafted tissues that have been labeled using Hoechst or other fluorescent dyes (e.g., 5). Transplantation of retrovirally infected avian tissue into a host embryo resistant to viral infection is a possibility in order to analyze the fate of cells carrying a transgene (6). Grafting of mouse tissue into a chick host has also been used to analyze developmental interactions between tissues of transgenic animals and that of the host embryo (7).

This chapter describes the procedure for grafting of neural tissues in general, and provides diagrams depicting grafting of rhombomeres as an example of this technique. Learning neural transplantation is a long and frustrating business, which requires many repetitions and probably weekly practice to achieve any success. However, many of the trivial problems of its execution can be overcome by the strategies outlined here. Grafting experiments can often provide a valuable adjunct to other studies, e.g., molecular biological or tissue-culture experiments, in exploring the role or interactions of a molecule or tissue region. In addition, they may be the method of choice for addressing some developmental problems, such as the state of determination of a tissue, its inductive influence, or to construct a fate map. This technique will therefore continue to provide a valuable tool for experimental embryologists.

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