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Genes are activated when transcription factors interact with specific DNA sequence elements to initiate a cascade of events, including chromatin remodeling, transcription and RNA processing. Although these steps are often studied as distinct mechanisms, they are, in fact, highly interdependent. To achieve an integrated view of gene expression, it is necessary to understand how they are coordinated at transcription sites. By combining advances in live-cell imaging and auto-fluorescent protein technology with reporter gene engineering, it is possible to visualize gene activation at specific transcription sites in single cells. The information provided by this experimental approach can lead to the discovery of novel regulatory mechanisms.
The Janicki laboratory has used this single-cell live-cell imaging to investigate mechanisms of transcriptional activation, replication independent histone H3.3 chromatin assembly and the functions of PML nuclear body factors. The long-term goal of the laboratory is to bridge the gap in our understanding of molecular mechanisms and cellular organization. The limits to our understanding of cellular regulation are directly related to the limitations of our experimental techniques. The ability to visualize molecularly defined transcription sites in single living mammalian cells now provides unprecedented access to information about the timing and spatial organization of transcription. Only by directly examining the dynamic interactions of factors with specific sequence elements will it be possible to fully understand how cells “translate” the information encoded in DNA into heritable patterns of gene expression.
The microscope in the image belonged to William E. Horner, M.D., a collaborator with Caspar Wistar, M.D., in the early 1800s.
Dr. Horner, a lecturer at the University of Pennsylvania, was a pioneer of the use of microscopes in anatomical and medical research. He authored Special Anatomy and Histology, a seminal text on the subject.