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Symposia
Invertebrate models to address fundamental questions in neurobiology
Chairs
Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB)
Part of the sustainability of in-depth basic research is the use of powerful and validated animal models that are inexpensive. The ease of manipulation, inexpensive maintenance, genetic amenability, combined with the relatively simple nervous systems of invertebrates provides the opportunity to investigate universal questions that cannot easily be addressed in mammalian systems. Indeed, studies in these models have provided fundamental information about conserved neurobiology processes and molecular pathways underlying nervous system disorders. This symposium aims to highlight, through concrete examples, how the use of invertebrate models can contribute to the understanding of key biological phenomena. The session proposed will include talks on diverse topics with a common denominator: the use of different invertebrate models. Since key elements of the biology of neurons and circuits are highly conserved throughout the animal kingdom, the mechanisms exposed in this symposium are likely to be universally crucial. We combine leader PIs from Argentina and USA that, despite being young, have made key contributions to their specific fields. We think that this initiative will contribute to foster invertebrate neuroscience research in the region, and will expose the audience to a plethora of tools devoted to addressing fundamental biological questions.
Speakers
Polarization vision as a source of visual contrast in arthropods
Martin Beron de Astrada
Instituto de Biociencias, Biotecnología y Biología Traslacional (IB3); Dpto. de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales; UBA
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The polarization of light is a light quality invisible for the human eye. However, the sensitivity to the angle of light polarization to enhance visual contrast has been recognized in a number of animals inhabiting aquatic environments. So far, the visual mechanisms underlying such capabilities remain unknown.
In the last couple of years we have studied the mechanisms underlying polarization vision in the crab Neohelice granulata. We have quantified animals’ escape response and changes in heart rate as indexes of visual sensitivity. By presenting polarized motion stimuli with only linear polarization contrast (no intensity or spectral contrast) we observed maximum animals’ responses when object and background polarizations were aligned with the vertical and horizontal orientations. The addition of polarization contrast to threatening intensity contrast stimuli enhanced significantly a low threshold alert response of the animals but produced no effect on higher threshold defensive behaviors.
In line with theoretical models, our results provide experimental evidence that crabs perform a two-channel (vertical/horizontal) computation to achieve polarization contrast vision. We will discuss how such a two channel system maximizes information acquisition in the animals’ natural environment together with the limitations that polarization information processing might have.
The Drosophila Ih channel shapes circadian rhythms and sleep through the control of neuronal bursting frequency
Nara Muraro
IBioBA-CONICET-MPSP, Argentina
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Circadian rhythms have been extensively studied in Drosophila, however, still little is known about how the electrical properties of clock neurons are specified. We have performed a behavioral genetic screen through the downregulation of candidate ion channels in the lateral ventral neurons (LNvs) and show that the hyperpolarization-activated cation current Ih is important for the behaviors that the LNvs command: temporal organization of locomotor activity and sleep. Using whole-cell patch clamp electrophysiology we demonstrate that small LNvs are bursting neurons, and that Ih is necessary to achieve the high frequency bursting firing pattern characteristic of both types of LNvs. Since firing in bursts has been associated to neuropeptide release, we hypothesized that Ih would be important for LNvs communication. Indeed, we demonstrate that Ih is fundamental for the recruitment of PDF filled dense core vesicles to the terminals at the dorsal protocerebrum and for their timed release, affecting the temporal coordination of circadian behaviors.
Actuating a memory: how C. elegans remembers a learned behavioral preference
Daniel Colón-Ramos
Department of Neuroscience, Yale University School of Medicine, CT, USA
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How different plasticity mechanisms act together in vivo and at a cellular level to transform sensory information into behavior is not well understood. We show that in Caenorhabditis elegans two plasticity mechanisms-sensory adaptation and presynaptic plasticity-act within a single cell to encode thermosensory information and actuate a temperature preference memory. Sensory adaptation adjusts the temperature range of the sensory neuron (called AFD) to optimize detection of temperature fluctuations associated with migration. Presynaptic plasticity in AFD is regulated by the conserved kinase nPKCε and transforms thermosensory information into a behavioral preference. Bypassing AFD presynaptic plasticity predictably changes learned behavioral preferences without affecting sensory responses. Our findings indicate that two distinct neuroplasticity mechanisms function together through a single-cell logic system to enact thermotactic behavior.
A clock-controlled vitamin A pathway in the brain mediates seasonal photoperiodic responsiveness in the monarch butterfly
Christine Merlin
Texas A&M University, USA
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Seasonal adaptation to changes in light:dark regimes (i.e., photoperiod) allows organisms living at temperate latitudes to anticipate environmental changes. The circadian system has been implicated in measurement and response to the photoperiod. Yet, the key molecular pathways linking clock genes or the circadian clock to insect photoperiodic responses remain largely unknown. We showed that inactivating the clock in the North American monarch butterfly using loss-of-function mutants for circadian activators and repressor abolishes photoperiodic responses in reproductive output. Transcriptomic approaches in the brain of monarchs raised in long and short photoperiods, summer monarchs, and fall migrants revealed a molecular signature of seasonal-specific rhythmic gene expression that included several genes belonging to the vitamin A pathway. Rhythmic expression of these genes was abolished in clock-deficient mutants, suggesting that the vitamin A pathway operates downstream of the circadian clock. Importantly, a CRISPR/Cas9-mediated loss-of-function mutation in the gene encoding the pathway’s rate-limiting enzyme, ninaB1, abolished photoperiod responsiveness independently of visual function in the compound eye and without affecting circadian rhythms. Together, these results provide the first genetic evidence that the clock-controlled vitamin A pathway mediates photoperiod responsiveness in an insect, a function that could be evolutionary conserved in animals.