Mouse Preimplantation Embryos and Oocytes as an In Vivo System to Study Transcriptional Enhancers

Abstract

Multicellular organisms, as opposed to their unicellular counterparts, face a unique problem in carrying out life-sustaining functions. Whereas, in unicellular organisms the same cell performs all the necessary functions, in multicellular organisms there is a division of labor: specific cell types carry out specific functions in a spatial and temporal manner. For example, as a fertilized mouse one-cell embryo divides, differentiates, and develops into a complete animal, it is crucial to express the right gene at the right time and by the right cell type. One of the important mechanisms by which multicellular organisms achieve such a goal is to regulate transcription of RNA polymerase II promoters through enhancers. Our present knowledge of the principles that regulate mammalian transcription, including the enhancer function, mainly stems from studies involving cell-free in vitro systems, or in vivo systems comprised of tissue culture cells or animal viruses. In fact, although a wealth of knowledge on the mechanism of RNA polymerase II trancription that occurs at the promoter site has been gained from in vitro systems consisting of purified transcription factors, most of these systems do not exhibit enhancer function, unless the template DNA is reconstituted into chromatin. Similarly, it has been relatively unknown how these principles apply in physiological processes that regulate, for example, the development of a fertilized one-cell embryo into an animal.