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Dr. Martienssen completed his PhD at the Plant Breeding Institute at Cambridge University with Dr. David Baulcombe, and post-doctoral training with Drs. Bill Taylor and Mike Freeling at the University of California at Berkeley before joining the faculty at Cold Spring Harbor Laboratory in 1989, where he was appointed senior... read morescientist and Professor in 1995. He has authored more than 120 papers in genetics and developmental biology. Dr. Martienssen has a longstanding interest in transposable elements (TEs), which were first discovered in maize by B. McClintock at Cold Spring Harbor. He demonstrated that the epigenetic regulation of genes when TEs integrate nearby strongly resembles, and may underlie heterochromatic position effect variegation. TEs constitute the majority of most genomes, especially in heterochromatic regions, and TE-based mechanisms may be responsible for genome-wide epigenetic regulation. Martienssen also maintains a strong interest in developmental biology, working with stem cell maintenance and organ polarity in plants. Key genes include the SANT domain gene ASYMMETRIC LEAVES1, and the cryptic RNase H gene ARGONAUTE1, which plays a central role in RNA interference (RNAi). The fission yeast Schizosaccharomyces pombe has only a single Argonaute gene, allowing Martienssen to demonstrate that RNAi is required for heterochromatic silencing and histone modifications in fission yeast, because heterochromatin (junk DNA) is transcribed but rapidly turned over by RNAi. Microarray analysis and large scale sequencing of small RNA has revealed that this process is conserved in plants, and is enhanced when repeats are arranged in tandem orientation. In 2003, Martienssen and co-authors were awarded the AAAS Newcomb-Cleveland prize for the 2002 Breakthrough of the Year in the magazine Science.