The 2011 Genetics Society of America Medal: John Carlson
Robert R. H. Anholt

IN his 1985 book “Late Night Thoughts on Listening to Mahler's Ninth Symphony,” Lewis Thomas reflected on the sense of smell and wrote: “I should think we might fairly gauge the future of biological science, centuries ahead, by estimating the time it will take to reach a complete, comprehensive understanding of odor.” Little could he have imagined that the seemingly intractable mystery of the sense of smell, which so intrigued him, would be solved and be crowned with a Nobel Prize within two decades. Neither could he have imagined that the olfactory system of the humble fruit fly Drosophila melanogaster would emerge as one of the best characterized and best understood olfactory systems. If he were alive today, Lewis Thomas would be the first to congratulate John Carlson from Yale University on receiving the Genetics Society of America (GSA) Medal, a well-deserved recognition for a sustained groundbreaking pioneering endeavor that led to the discovery of a family of about 60 odorant receptors expressed in the antennae and maxillary palps of Drosophila, characterization of the functional organization of their expression, and characterization of their molecular response profiles and activation kinetics.

Carlson's early work in the laboratory of David Hogness at Stanford University led to the discovery of the Jonah multigene family. Soon, thereafter, after establishing his laboratory at Yale University, Carlson directed his attention to the olfactory system of Drosophila. At first, he used conventional enhancer trap studies and P-element mutations in attempts to gain a foothold that would enable him to make progress in understanding the mechanisms of odor recognition and olfactory signaling. But the big breakthrough came in 1999 when his laboratory identified the family of Drosophila odorant receptors. Carlson set out to meticulously study the molecular response profiles of these receptors and discovered that pairs of neurons that express particular receptors always occur together in the same sensilla. He proceeded to characterize their molecular response profiles using single unit recording in the maxillary palps and the antenna. A second major breakthrough was the discovery of a mutant that failed to express the Or22a receptor in otherwise intact chemosensory neurons. Carlson showed that any odorant receptor could be expressed in this “empty neuron” while retaining its native properties, thereby establishing a powerful bioassay that could be used to characterize molecular response profiles of both adult and larval odorant receptors. He also used this ingenious approach to characterize response profiles of the odorant receptor repertoire of the malaria mosquito Anopheles gambiae in a seminal paper published in Nature that received widespread attention from the national press. In addition to other wide-ranging studies on Drosophila chemosensation, Carlson has recently made major advances to understanding how different transcription factors might regulate how each chemosensory neuron chooses to express an individual odorant receptor from among its chemoreceptor repertoire.

During the course of his amazing discoveries John Carlson never neglected his job as a mentor. Virtually every single one of his students or postdoctoral fellows has received awards for presentations at scientific conferences, including the GSA annual Drosophila genetics conferences, and all were able to pursue successful academic careers, in large part due to his outstanding training and unwavering support. The term “gentleman and scholar” certainly applies to this most worthy recipient of the GSA Medal.

John Carlson (Photo by Jerry Domian)