09:00-09:30
Acoustic communication and evolution in Drosophila: roles for a nuclear receptor and its regulon
Dr Joerg Albert
Abstract
All behaviour is guided, or restricted, by the senses. Sense organs have evolved in multiple ways to extract and pre-process information from the external world. However, molecular mechanisms of sense organ specification and their evolutionary origins have remained unclear. We have used closely-related Drosophila species to explore how ears can contribute to evolution - and how evolution, in turn, has shaped ears.
In flies (Diptera), hearing is mediated by Johnston’s Organ (JO) neurons in the second antennal segment (1). In Drosophilids, the spectral tuning of the flies’ antennal ears correlates with the spectral composition of song pulses produced by conspecific males (2). Laser-Doppler vibrometric analysis of sound receiver mechanics and extracellular recordings of compound action potentials from the antennal nerve show that the species-specific auditory tuning is partly the result of variations in the molecular modules for mechanotransduction in JO neurons.
RNA-Seq based transcriptomics of the JOs from six closely-related Drosophila species combined with predictive bioinformatics (i-cisTarget and iRegulon) identified a particular type of transcription factor from the nuclear hormone receptor family as important contributor to inter-specific variation in Drosophilid ears.
Nuclear hormone receptor proteins are also required for normal sex organ development. The investigated mutants showed sexually dimorphic defects in auditory function (both with regard to auditory mechanics and auditory nerve responses). On the sender side of Drosophila acoustic communication, in turn, mutant males displayed severe defects in song production (both in their propensity to produce songs and with regard to song structure). The duality of its contributions presents this nuclear receptor gene as a potential substrate for genetic coupling in the Drosophila acoustic communication system.
09:40-10:10
Making an effort to listen: mechanical amplification by ion channels and myosin motors in hair cells of the inner ear
Professor Jim Hudspeth, The Rockefeller Univeristy, USA
Abstract
Human hearing is enhanced by an active process that amplifies the ear's mechanical inputs several hundredfold, sharpens frequency tuning to allow the discrimination of tones differing in frequency by less than 0.2 %, and compresses six orders of magnitude in the amplitude of sounds into only two orders of magnitude in neural output. In addition, spontaneous otoacoustic emissions emerge from ears in a very quiet environment, an indication that the active process can be so exuberant as to become unstable. Cooperativity between mechanoelectrical-transduction channels confers negative stiffness on the hair bundle, which together with myosin-based adaptation motors elicits a dynamical instability that underlies the active process. Experiments on individual hair bundles indicate that the bundle's operation near this instability, a Hopf bifurcation, accounts for the four characteristics of the active process.
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Professor Jim Hudspeth, The Rockefeller Univeristy, USA
Professor Jim Hudspeth, The Rockefeller Univeristy, USA
Born and raised in Houston, Texas, Jim Hudspeth conducted undergraduate studies at Harvard College and received PhD and MD degrees from Harvard Medical School. Following postdoctoral work at the Karolinska Hospital in Stockholm, he served on the faculties of California Institute of Technology, University of California, San Francisco, and University of Texas Southwestern Medical Center. After joining Howard Hughes Medical Institute, Jim moved to Rockefeller University, where he is F. M. Kirby Professor. Dr. Hudspeth conducts research on hair cells, the sensory receptors of the inner ear. He and his colleagues are especially interested in the active process that sensitizes the ear, sharpens its frequency selectivity, and broadens its dynamic range. They also investigate the replacement of hair cells as a potential therapy for hearing loss. Jim is a member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society.
10:40-11:10
Novel synaptic transmission from vestibular hair cells to calyceal afferents serves fast reflexes in amniotes
Professor Ruth Anne Eatock
Abstract
The vestibular type I hair cell and its distinctive calyceal synapse are found only in the inner ears of reptiles, birds and mammals. Like the cochlea, the type I – calyx synapse may represent adaptations to life on land. Over the past 20 years, evidence has accrued that these unusual-looking synapses are also functionally remarkable, featuring not just chemical (quantal) transmission of vesicle-bound glutamate from ribbon synapses but also a form of non-quantal transmission that depends on currents through ion channels in dense arrays on presynaptic (hair cell) and postsynaptic (calyceal) membranes. Quantal and non-quantal transmission filter the transmitted mechanosensory signal in distinct ways and have been recorded both together and separately, suggesting unexpectedly rich possibilities for shaping vestibular inputs to the brain.
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Professor Ruth Anne Eatock
Professor Ruth Anne Eatock
Ruth Anne Eatock was introduced to comparative neurobiology of the auditory system by Geoff Manley, who supervised her undergraduate and Master’s theses at McGill University. These studies stimulated an interest in hair cell physiology, and for her doctoral research she worked with Jim Hudspeth at Caltech on sensory adaptation in vertebrate hair cells. As a postdoctoral fellow, she studied the dependence of auditory nerve fiber firing rate on sound pressure level in the alligator lizard, a model system developed by Tom Weiss of MIT and the Eaton-Peabody Laboratory. Ruth Anne held academic positions at the University of Rochester in New York, Baylor College of Medicine in Houston, and Harvard Medical School before arriving at the University of Chicago in 2014. Her research has focused on developing and mature function in vestibular hair cells and afferent synapses of diverse vertebrates, especially rodents.
11:20-11:50
The role of the auditory brainstem in understanding speech in challenging listening conditions
Dr Tobias Reichenbach, Impertial College London, UK
Abstract
Humans excel at selectively listening to a target speaker in background noise such as competing voices. While the encoding of speech in the auditory cortex is modulated by selective attention, it remains debated whether such modulation occurs already in subcortical auditory structures. Investigating the contribution of the human brainstem to attention has, in particular, been hindered by the tiny amplitude of the brainstem response. Its measurement normally requires a large number of repetitions of the same short sound stimuli, which may lead to a loss of attention and to neural adaptation. This talk describes a mathematical method to measure the auditory brainstem response to running speech, an acoustic stimulus that does not repeat and that has a high ecological validity. This research employs this method to assess the brainstem's activity when a subject listens to one of two competing speakers, and show that the brainstem response is consistently modulated by attention.
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Dr Tobias Reichenbach, Impertial College London, UK
Dr Tobias Reichenbach, Impertial College London, UK
Dr. Tobias Reichenbach is a Senior Lecturer (US equivalent: Associate Professor) at the Department of Bioengineering at Imperial College London. He joined Imperial in 2013 after postdoctoral training in computational neuroscience and the biophysics of hearing with Dr. A. J. Hudspeth at the Rockefeller University in New York. He graduated in 2008 with highest honors from the Ludwig-Maximilians University in Munich, Germany, where he researched on theoretical aspects of non-equilibrium pattern formation and statistical physics in the group of Dr. E. Frey.
Dr. Tobias Reichenbach is interested in problems at the interface of physics and biology. He uses ideas from theoretical physics, mathematics, computer science and experimental neruobiology to investigate how biological systems function, with a particular focus on the auditory system. Dr. Reichenbach aims at applying his findings in the developement of novel, biologically-inspired technology.