August 2013

James E. Darnell’s “Reflections”

A brief history of the discovery of RNA and its role in transcription — peppered with career advice

James DarnellJames Darnell begins his Journal of Biological Chemistry “Reflections” article by saying, “graduate students these days have to swim in a sea virtually turgid with the daily avalanche of new information and may be momentarily too overwhelmed to listen to the aging. I firmly believe how we learned what we know can provide useful guidance for how and what a newcomer will learn.” Considering his remarkable and groundbreaking discoveries in RNA processing and eukaryotic transcriptional regulation spanning 60 years of research, the “aging” Darnell’s advice should be cherished.
 
When Darnell started medical school at Washington University School of Medicine in St. Louis, there were two local Major League Baseball teams. (The Browns left for Baltimore three years later in 1954.) It was during his second year at medical school, while studying streptococcal disease in Robert J. Glaser’s laboratory, that Darnell realized he “loved doing the experiments” and had his first “career advancement event.” He and technician Barbara Pesch discovered that in vivo penicillin treatment killed streptococci only in the exponential growth phase and not in the stationary phase. These results were published in the Journal of Clinical Investigation and earned Darnell an interview with Harry Eagle at the National Institutes of Health.
 
Darnell arrived at the NIH in 1956, shortly after Eagle had shifted his research interest to culturing animal cells in vitro. His culture medium, Eagle’s minimal essential medium, is still used by millions of scientists worldwide. Since Eagle was at that point focused on cell metabolism, he suggested that Darnell take up a side project on poliovirus replication in mammalian cells in collaboration with Robert I. DeMars. It turned out that DeMars’ Ph.D. adviser was also the adviser of James Watson (of double-helix fame), so Darnell met Watson, who invited him to give a talk at Harvard University. Darnell subsequently was offered a job as an assistant professor at the Massachusetts Institute of Technology by Salvador Luria (Watson and DeMars’ adviser). A take-home message is to embrace side projects, because you never know where they may lead: In Darnell’s case, such a project helped to shape the rest of his career.
 
Darnell arrived in Boston in 1961. Following the discovery of DNA’s structure in 1953, the world of molecular biology was turning to RNA in an effort to understand how proteins are made. Darnell’s background in virology (it was discovered in 1960 that viruses used short-lived RNA to replicate) was ideal for the aim of his first independent lab: exploring mRNA in animal cells grown in culture. While at MIT, he developed a new technique for purifying RNA along with making other observations suggesting that nonribosomal cytoplasmic RNA may be involved in protein synthesis.
 
In 1964, Darnell moved to Albert Einstein College of Medicine for full professorship and a generous 250-percent salary increase. (He notes that by this time he had a wife and three sons.) By this time it was hypothesized that heterogenous nuclear RNA was a precursor to mRNA, but the experiments to demonstrate this were encountering difficulties. At Einstein, Darnell discovered RNA processing of pre-tRNAs and demonstrated for the first time that a specific nuclear RNA could represent a possible specific mRNA precursor.
 
In 1967 Darnell took a position at Columbia University, and it was there that he discovered (simultaneously with two other labs) that mRNA contained a polyadenosine tail. The three groups all published their results together in the Proceedings of the National Academy of Sciences in 1971. Shortly afterward, Darnell made his final career move four short miles down the street to Rockefeller University in 1974.
 
Over the next 35-plus years at Rockefeller, Darnell never strayed from his original research question: How do mammalian cells make and control the making of different mRNAs? His work was instrumental in the collaborative discovery of splicing in the late 1970s and in identifying and cloning many transcriptional activators. Perhaps his greatest contribution during this time, with the help of Ernest Knight, was the discovery and cloning of the signal transducers and activators of transcription (STAT) proteins. And with George Stark, Andy Wilks and John Krowlewski, he described cytokine signaling via the JAK-STAT pathway. Darnell closes his “Reflections” with perhaps his best advice: Do not get too wrapped up in your own work, because “we are all needed and we are all in this together.”

Joseph TianoJoseph P. Tiano (tiano233@hotmail.com) is a postdoctoral fellow at the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Md.


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