High Resolution Gene Expression Analysis in Mice Using Genetically Inserted Reporter Genes

Detailed analysis of the temporal and spatial patterns of expression of a gene in situ can provide a wealth of knowledge regarding the potential functional roles of a gene product. However, such detailed analysis of gene expression patterns represents a great challenge to biologists. Classical approaches such as northern blotting, RNAse protection, PCR assays and western blotting are highly reliable and sensitive means of detecting expression, but thesemethods completely lack spatial information indicating where the gene is expressed. Spatial information can be obtained by the use of similar approaches such as in situ hybridization and immunohistochemistry on tissue sections or whole tissue preparations. These methods, however, are limited by the availability of robust and reliable probes for the gene of interest as well as the availability of appropriately prepared tissues to probe. Even under optimal conditions, such approaches are not practical when the aim is to undertake an exhaustive screen to discover rare sites of expression in a range of ages. The use of genetically inserted reporter genes with optimal detection characteristics, most notably the bacterial LacZ gene encoding ˇgalactosidase (ˇ-Gal), in vivo by either targeted or transgenic insertion, allows one to screen a diverse array of tissues and developmental stages rapidly and easily, and to observe domains of expression with extremely high resolution. Coupling of reporter gene insertion with gene targeting and inactivation in mice represents an extremely powerful tool for elucidating gene function, allowing high resolution analysis of domains of expression coupled with the potential loss-of-function phenotypes of the gene of interest. This approach has been used with a great deal of success over the past 10 years in genetargeting, and considerably longer (but without the phenotypic component and with significant limitations) using