Cell lineage analyses trace the hierarchy of cell types derived from a progenitor population. Critical to these analyses is the ability to track reliably all or defined subsets of the clonal descendants of the progenitor population. This necessitates marking the cells with a heritable and cell autonomous marker. Transgenes encoding molecules that can be visualized directly in situ without compromising cell differentiation, such as the reporter, P-galactosidase encoded by lacZ, and chloramphenicol acyltransferase, encoded by the CAT gene are the most widely used.

lacZ can be readily detected using a sensitive histochemical assay such that cells in which the P-galactosidase gene is transcriptionally active produce a blue stain in tissue sections or in whole mounts (1). Some lineage studies demand the simultaneous detection of the lacZ product and other tissue-specific proteins or transcripts. In this chapter, we discuss the experimental strategies in which the lacZ transgene can be utilized in the analysis of cell lineages, and we detail assays for detecting P-galactosidase by X-gal histochemistry or immunological localization of the enzyme in combination with mRNA in situ hybridization, immunochemistry, and histochemical procedures, such as alkaline phosphatase staining.

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