Transgenic Analysis of Embryonic Gene Expression Using LacZ as a Reporter

Abstract

Determining the expression pattern of a gene is often the first step in defining its function. The analysis of expression during mammalian embryonic development can present a challenge if the gene of interest is expressed for only a short interval of time, or in a small number of cells. In situ hybridization and immunological staining are the established methods by which expression analysis is usually accomplished, but both are laborious, require a purified probe for optimal detection, and often require sectioning of the embryo. An alternative method for determination of the expression pattern involves the use of a reporter to mark the gene of interest. Detection of the reporter protein itself, or of its enzymatic activity following histochemical staining, provides a way to trace expression of the marked gene. The bacterial lacZ gene, which encodes the enzyme β-galactosidase (Wallenfels and Malhotra 1960), has proved to be very useful as a reporter gene. β-galactosidase cleaves its substrate 5-bromo-4-chloro-3-indolyl-β-D-galactoside (X-Gal) to yield a blue reaction product which precipitates in the cell. β-galactosidase is well suited as a reporter for a number of reasons including:

• Its rapid and simple enzymatic assay

• Its ability to be assayed and detected in situ

• Its cell autonomy, allowing detection in single cells

• Its sensitivity as a marker of gene activity.