Site Specific Recombinases: Cre & Genetic Reporters
Several site-specific recombinases exist, such as FlpE, Flpo, Phi31c, Cre and now Dre (among others). Our lab's principal interest in these arises from the ability to ablate a gene of interest's function in a temporally and spatially restricted manner (or "conditionally knockout"). For this type of technology, the SSR Cre, and its target sequence loxP, has been the default method of choice for several biologists.
A second reason we are interested in SSRs is because we are curious about cellular differentiation and the contribution of early progenitor cells to the developing embryo and adult. Accordingly, being able to visually identify early progenitors (or distinct populations) of cells and their descendants in a heritable, permanent fashion is highly desirable. This type of experiment is referred to as a genetic lineage tracing. For an excellent review on various lineage tracing strategies, see this paper from Buckingham and Meihlac, 2011.