Out Fishing:
The ability to disrupt, or knock out, a specific gene in ES cells and mice was developed in the late 1980s, and the use of knockout mice has led to many insights into human biology and disease8-11. Current technology also permits insertion of ‘reporter’ genes into the knocked-out gene, which can then be used to determine the temporal and spatial expression pattern of the knocked-out gene in mouse tissues. Such marking of cells by a reporter gene facilitates the identification of new cell types according to their gene expression patterns and allows further characterization of marked tissues and single cells.