Beta-Galactosidase as a Transgenic Reporter for the Mapping and Phenotyping of MT1 and MT2 Melatonin Receptor-Expressing Cells.

Genetic technology allows inserting transgenic reporters such as beta-galactosidase (LacZ) into the loci of the Mtnr1a (MT1) and Mtnr1b (MT2) receptor genes to track MT1 and MT2 melatonin receptor expression. Given the limited sensitivity of nonradioactive in situ hybridization and the problematic specificity of existing melatonin receptor antibodies for immunohistochemistry, this new technology is a key tool to study the localization and the phenotypes of cells expressing melatonin receptors. Here we describe two protocols to detect transgenic LacZ expression driven by the MT1 or MT2 promoters either by the enzymatic activity of the transgenic LacZ enzyme or by using specific antibodies against LacZ with immunohistochemistry. This approach has already yielded a detailed mapping of both MT1 and MT2 expression in the mouse brain and retina. Furthermore, we also phenotyped some of the most important types of cells expressing these two melatonin receptors.