Stephen F. Heinemann (1939–2014)
Authors: Ana Belén Elgoyhen, Geoffrey T. Swanson, Christophe Mulle
Journal: Neuron (2014)

Steve Heinemann, one of the fathers of modern molecular neuroscience and a pioneer in neurotransmitter receptor biology, passed away on August 6, 2014, in La Jolla, California. Steve was well known in the neuroscience community as a genuinely nice guy with an unorthodox approach to research. For almost four decades in an extraordinarily productive career he helped to drive a quantum leap forward in elucidating the molecular components and cellular basis of excitatory neurotransmission in the mammalian CNS. These efforts paved the way for new insights into fundamental aspects of nervous system function, which led to advances in our understanding of neurological and psychiatric disorders. Born in Boston in 1939, Stephen Fox Heinemann obtained a bachelor in science degree from the California Institute of Technology in 1962. He pursued his PhD in biochemistry at Harvard University in 1967 under the mentorship of Matthew Meselson, where he studied the structure of DNA. His postdoctoral training was carried out at the Massachusetts Institute of Technology and Stanford University School of Medicine, during which time he made contributions to the understanding of the genetics of the bacteriophage lambda life cycle. Soon after, his interest shifted to the nervous system, and he joined the Salk Institute for Biological Studies in 1970, where he became one of the founders of the Molecular Neurobiology Laboratory at the newly minted research institute that would become his second home. The Salk Institute, a masterpiece of Louis Kahn, one of the most influential architects of the 20th century, was designated a historical landmark in 1991, following his father’s “even a brick wants to be something” prophecy. A similar destiny was to be followed by the Molecular Neurobiology Laboratory, a program to be ranked number one in world neuroscience in the late 1980s, in part due to discoveries arising from the Heinemann laboratory. In his early days at the Salk Institute, Steve focused on the neurotransmitter receptors present at the neuromuscular junction. This was the model system widely used to understand synaptic transmission before brain synapses became tractable. His landmark early work, in collaboration with Jon Lindstrom and others, established that myasthenia gravis, a disease that leads to muscle weakness, fatigue, and paralysis, is the consequence of the presence of autoantibodies to nicotinic acetylcholine receptors (nAChRs) present at the neuromuscular junction. Steve’s primary interest, however, was to understand the structure and properties of these acetylcholine receptors. In 1970, Jean-Pierre Changeux and coworkers used biochemical methods to characterize the nAChR as a ligand-gated ion channel formed by five homologous subunit proteins. In order to isolate DNA complementary to the mRNA encoding specific receptor subunit proteins, Steve decided to use a strategy based on recently developed molecular cloning methods. Biochemical methods had previously yielded short stretches of amino acid sequences from one of the muscle nAChR proteins; using this information, one could clone the full-length sequence encoding channel subunits from a suitable library of cDNAs. He was on the right path, but just not on time, because in 1982 a research group led by Shosaku Numa cloned the first cDNA encoding a nAChR subunit from the electric organ of the ray Torpedo californica. Having just lost a battle, but not the war, Steve turned his attention to brain ligand-gated ion channels together with Jim Boulter and Jim Patrick. The scarcity of the nAChR protein in the brain precluded biochemical derivation of partial peptide sequences, however, and a different tactic was required. Relying on the assumption that neuronal nAChRs should have some degree of identity with receptor subunits present at the neuromuscular junction, and using low-stringency molecular hybridization techniques, the Heinemann group was able to clone the first neuronal nicotinic receptor subunit, which is now named α3. This was followed by the cloning of the entire family of neuronal nicotinic receptor α and β subunits, the characterization of channel properties when expressed in heterologous systems, and the differential distribution of receptor subunits in the brain. Finally, in 1994 the α9 nicotinic cholinergic receptor was cloned in the Heinemann laboratory, deciphering the molecular identity of the cholinergic receptor that mediates efferent inhibition of sound amplification within the inner ear. The nicotinic receptor subunit clones were immediately licensed to the pharma industry for the development of drugs to be used in neurological disorders and tobacco addiction. As increasing numbers of nicotinic and the structurally related GABA receptor subunit cDNAs began to yield to maturing techniques in molecular neuroscience, a new set of targets became the object of a feverish cloning race between several laboratories, including that of Steve Heinemann, in the late 1980s and early 1990s. These receptors were, of course, those that mediated excitatory signaling in the CNS, the ionotropic glutamate receptors (iGluRs). The excitement about glutamate receptors was at its climax during this period because of the role they were thought to play in neurological disorders such as stroke, ischemia, or slowly progressing neurodegenerative diseases. The straightforward application of low-stringency hybridization with probes based on other neurotransmitter receptor proteins was a fruitless endeavor, for reasons which became clear after the cloning of the first glutamate receptor by Michael Hollmann in Steve’s laboratory. Michael chose the very laborious approach known as “expression cloning,” which relied on the detection of receptor currents (in this case, evoked by the agonist kainic acid) following injection of appropriate RNAs into Xenopus oocytes, which was a novel approach that had been recently developed by Ricardo Miledi. Armed with a library of cDNAs prepared from rat brain tissue, Hollmann’s persistent and sustained effort chased a small, perhaps initially unconvincing kainate-evoked depolarization through ever-smaller pools of unique cDNAs, and ultimately yielded the first iGluR subunit to be cloned, which they named GluR-K1. We now refer to this AMPA receptor subunit as GluA1, and its cloning led to a tense race to the finish within the Heinemann laboratory and with other laboratories, most particularly that of Peter Seeburg at the University of Heidelberg, to clone other AMPA receptor subunits and the related kainate and NMDA receptors. This initial cloning feat was obviously a gold mine that led to numerous secondary areas of exploration and discovery. For example, the precise topology of the receptor subunits in the plasma membrane was an unexpected matter for debate. The shared structural template for other ligand-gated neurotransmitter receptors, nAChRs, and GABAA receptors naturally led to the expectation that iGluRs would be constructed on similar principles. This turned out not to be the case; however, using a set of opportune mutants of recombinant receptors, Steve’s laboratory demonstrated iGluRs only had three transmembrane domains plus a cytoplasm-facing re-entrant membrane loop. The cloning of iGluR subunit cDNAs also yielded an ancillary surprise when it was discovered by the Seeburg and Heinemann laboratories that cellular mechanisms exist to change the encoded sequence of some receptor subunit genes, now referred to as RNA editing, which in the case of AMPA and kainate receptors has profound functional consequences. While the stakes during and subsequent to the iGluR cloning race were obviously quite high, Steve appreciated this competition not as a threat, but instead as a compelling source of motivation and occasional amusement, and in later days the high drama and tension of these pivotal times grew to mythological proportions. The cloning efforts led by the Heinemann laboratory also confirmed earlier pharmacological studies that implicated kainate receptors as a subfamily of iGluRs distinct from AMPA receptors (or “quisqualic receptors,” as they also were known earlier), and therefore signaled the end to the dysmorphic appellation of “non-NMDA” or “AMPA/kainate” receptors that was in common use. Steve enthusiastically supported all attempts from his fellow collaborators to understand the functional relevance of these newcomers. It soon appeared that the gene-targeting approach in mice, which was still in its infancy, was particularly suited to decipher the mysteries of this receptor family, because many conventional approaches proved problematic (and some, such as the development of selective anti-subunit antibodies, remain so). Knockout mice from all kainate receptor subunits produced in Steve’s laboratory finally revealed their peculiar and unexpected roles in the regulation of activity of hippocampal circuits. The newly cloned glutamate receptors and these unique mouse models were undeniably valuable resources for many neurobiologists working on mammalian synaptic function and plasticity, and Steve Heinemann was exemplary in his commitment to making these tools accessible to as many laboratories as possible. The myriad of acknowledgments in studies from scientific reports, originating from laboratories all over the world, make clear that his remarkable generosity greatly contributed to the swift progress in understanding neurotransmitter receptors and synaptic mechanisms over the last three decades. This undoubtedly includes many new therapeutic avenues for pharmaceutical and biotechnological companies to search for cures in the treatment of “synaptopathies” such as stroke, epilepsy, Parkinson’s and Alzheimer’s diseases, as well as neuropsychiatric conditions. Steve’s most recent work highlights the broadness of his views and his continuous interest in the mysteries of the normal and diseased brain, from astrocytes and oscillations in recognition memory to nicotinic receptors in Alzheimer’s disease. In addition to leading his laboratory, Steve was an active member of the greater scientific community and received a number of awards and honors for his research accomplishments. Most notably, he was elected president of the Society for Neuroscience from 2005 to 2006. He was also a member of the National Academy of Sciences, the National Institute of Medicine, and the American Academy of Arts & Sciences. He received the Bristol-Myers Squibb Distinguished Achievement in Neuroscience Research Award and the McKnight Award for Research. In 2010, he was awarded the Julius Axelrod Prize for exceptional achievements in neuropharmacology and exemplary efforts in mentoring young scientists. In this regard, Steve leaves a wide-reaching scientific legacy that includes not only his seminal contributions to our understanding of the molecular identity and function of nicotinic cholinergic and glutamate receptors, but also shaping the course of neuroscience in the US and the world during a time of acute interest in all aspects of brain function. On a more personal level, the hundred-plus “Heinemaniacs” who comprised his laboratory over the many years of its existence were challenged by the free-wheeling nature and abundant possibilities that were intrinsic to life as a member of Steve’s team. He created a uniquely anarchic environment that fostered creative, competitive, and rigorous science limited only by imagination. “Stevie” was a generous mentor and colleague, a courageous man of contagious energy and enthusiasm, and an adventurous and bright scientist who was always open for a spirited debate about interpretation of data, research at large, and the vagaries of success and failure, or even politics. He did not shy away from the latter when principle was involved, as was the case when, as the incoming President of the Society for Neuroscience, he helped to organize a controversial “Dialogues Between Neuroscience and Society” lecture by the Dalai Lama at the 2005 annual meeting. He was a natural storyteller with an endless supply of entertaining and occasionally absurd anecdotes from his scientific and personal life, many of them drawn from adventures during his hiking trips and excursions into the backcountry of Baja California and farther afield. Steve appeared to us at heart to be a rebel, fighting against authority in its various forms with a sense of amusement and mischievousness, even when he himself was the authority in question. As a nominee for President of the Society for Neuroscience, for example, he campaigned within the laboratory for votes—for his rival. Steve epitomized the principle that, at its core, scientific research should be a fun pursuit as well as intellectually stimulating, and he demonstrated by his actions that success at the highest levels could be achieved without compromising principles or losing sight of those most important aspects of life. It is difficult now to imagine the Salk Institute without Steve Heinemann, but it is clear that his legacy will continue to flow forward into the future, a scientific manifestation of the “stream of knowledge” that famously bisects the central courtyard of the Salk Institute en route to the endless horizon of the Pacific Ocean.