Laser Ablation and Fate Mapping

Much of the information about the fate and function of embryonic cell populations was gained in the early years of experimental embryology through ablation studies. With the advent of more sophisticated marking techniques using interspecific chimeras and molecular markers, ablations were generally abandoned because of the problems of misinterpretation of data when unforeseen reconstitution of cell populations occurred following ablation. This is reminiscent of the problems with interpretation of the first generation of gene knockouts where other genes in a family surreptitiously reconstitute the function of the disabled gene. However, even with the problem of data interpretation, useful information can be obtained from ablation experiments when they are properly controlled and conservatively interpreted as has happened for the global null gene mutations. Our group has particularly benefited from ablation technology, because it has provided a clinically relevant model system to explore with a number of interesting approaches. Because of our group’s need for a large number of embryos with particular ablations, we have established a largely automated system for production of uniform neural crest ablations in chick embryos. The system, which is relatively simple, consists of a stereomicroscope-mounted laser and motorized micropositioner, which are both controlled by a computer (see Fig. 1 ). Very precisely placed ablations can be done by relatively unskilled lab personnel with a minimum of actual hands-on time. In addition, it is possible to graft tissue or cultured cells into the ablation site for tracing or cell lineage studies (see Note 1 ).