Life and Science in the RNA World
Like a number of other present and former faculty in this department, Dr. Stephen Munroe majored in chemistry as an undergraduate. For graduate work he went to Indiana University, where there was a well-established biochemistry program within the Department of Chemistry. However, his interests quickly turned to molecular biology as he studied the biosynthesis of tubulin on polysomes isolated from rat brain. This marked the beginning of his career-long interests in RNA and RNA-protein complexes.
Following completion of his Ph.D., Munroe spent three years at the Genetics Division of Children’s Hospital Medical Center in Boston, studying changes in chromatin structure associated with DNA replication, a fascinating problem in light of the recent discovery of nucleosome structure. A final post-doctoral year at the Worcester Foundation for Biomedical Research outside Boston provided an opportunity to study RNA-protein interactions associated with nuclear RNA, a timely undertaking that coincided with the unexpected discovery in 1977 of mRNA splicing in adenovirus-infected cells. With the encouragement of his postdoctoral mentor, Dr. Thoru Pederson, Munroe devoted the last several months of his postdoctoral work to learning methods for isolating nuclear ribonucleoprotein complexes associated with adenovirus RNA. So it was with stocks of virus and HeLa cell cultures packed in dry ice that he arrived at Marquette University on a very hot Labor Day weekend in 1978.
The timeliness of the project Munroe brought with him to Marquette led to early funding by the NIH and later the NSF. Munroe was joined in the lab by several graduate students, Michael Banker, Cynthia Mengle and Mark Maffitt, who helped develop various molecular methods for characterizing RNA-protein interactions in the cell nucleus. Another associate of Munroe at this time was Deborah Meuler, a graduate of Marquette who had recently completed her Ph.D. at Indiana University . Together Munroe and Meuler succeeded in establishing the in vitro cell-free system for splicing radiolabeled RNA, recently pioneered by Adrian Krainer while working with Dr. Thomas Maniatis at Harvard. Munroe used this system to study structural requirements for splicing of adenovirus mRNA with the addition of a complementary antisense RNA. These experiments had two interesting results. First, the antisense RNA complementary to exons proved to be an efficient inhibitor of splicing, suggesting that exon sequences as well as those at splice sites themselves, were critical for splicing. Second, the observation that proteins within the nuclear extract, including those associated with nuclear pre-mRNA, rapidly catalyze RNA-RNA base pairing also proved very interesting and was the precursor to studies in many other laboratories on RNA chaperones. Both observations were expanded during a year-long sabbatical (1987-88) at Cold Spring Harbor Laboratory where Munroe worked closely with Adrian Krainer and Dr. Richard J. Roberts, one of the original discoverers of mRNA splicing (and in 1993 a recipient of the Nobel Prize in Medicine).
On returning to Marquette, Munroe continued this work with Xiaofan Dong, a graduate student who received an MS degree for her work on protein-catalyzed RNA-RNA annealing. At the same time he began to investigate the role of naturally occurring antisense mRNAs associated with the expression of mRNA for the thyroid hormone receptor (TRα) and Rev-erbα, the latter a nuclear receptor protein discovered by Dr. Mitchell A. Lazar in Dr. William W. Chin’s laboratory at Harvard. Munroe and Lazar thus began a collaboration that has extended to the present time. Major contributions to this work were made by Michelle L. Hastings and Hema Ingle, two graduate students. On receiving her Ph.D., Michelle joined Krainer’s lab at Cold Spring Harbor where Munroe had worked a decade before. After a long and productive stay in the Krainer lab, Michelle returned to the Midwest to establish her own, very active lab at Rosalind Franklin University in North Chicago, not far from Milwaukee, where she studies the role of splicing defects associated with genetic diseases.
Other graduate and undergraduate students have since contributed to the study of splicing and antisense RNA. These include Valerie Salato, who now works at Medical College of Wisconsin, and Chao Zhang. Among many talented undergraduates were Brandon Rindfleisch and Michael Scott Brown who spent two years characterizing TRα/Rev-erbα expression in marsupial mammals, an evolutionary approach that was recently extended by Chris Morales and Cynthia Aguilar, who helped sequence these same genes in the platypus.
Another line of Munroe’s work includes collaboration with Dr. Jun Zhu, a former graduate student of Adrian Krainer, with whom Munroe worked with during a sabbatical year in Dr. George Church’s lab at Harvard. Dr. Zhu and Munroe investigated the expression of antisense RNAs throughout the genome using a custom-designed microarray. These genome-wide investigations with Dr. Zhu, who is now at the NIH, have recently led to a three-way collaboration with Dr. James Anderson’s laboratory. Anderson’s pioneering work at Marquette on RNA-turnover via the TRAMP complex in yeast has provided novel insights into the metabolism of non-coding RNAs.
Munroe’s interests in RNA and RNA-protein interactions are reflected in his regular participation in the annual meetings of the RNA Society. This meeting frequently includes a number of Marquette graduates, not least Dr. Cindy L. Will, a native of Milwaukee who has worked on the mechanism of mRNA splicing in Germany for many years. Cindy was an undergraduate majoring in Biology in this department about the time when Munroe first arrived in Milwaukee. Recent meetings have included a number of other former Marquette biology students: Dr. Frank Rigo, now a researcher at Isis Pharmaceuticals, a biotech company specializing in the development of antisense therapeutics, as well as Will Mueller and Megan Mayerle, graduate students at the University of California-Irvine and Johns Hopkins, respectively.
Members of the RNA Society often refer to the “RNA World,” both as a hypothetical step in the evolution of life on earth and as an association of “ribo-philes,” scientists who enjoy the study of RNA in its many, often surprising roles in the cell.