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Abstract
Polyamines are essential polycations present in all living cells. Polyamine levels are maintained from the diet and de-novo synthesis, and their decline with age is associated with various pathologies. Here we found that polyamine levels oscillate in a daily manner. Both clock- and feeding-dependent mechanisms regulate the daily accumulation of key enzymes in polyamine biosynthesis through rhythmic binding of BMAL1:CLOCK to conserved DNA elements. In turn, polyamines control the circadian period in cultured cells and animals by regulating the interaction between the core clock repressors PER2 and CRY1. Importantly, we show that the decline in polyamine levels with age in mice is associated with a longer circadian period that can be reversed upon polyamine supplementation in the diet. Our findings suggest a cross talk between circadian clocks and polyamines biosynthesis that participate in circadian control, and open new possibilities for nutritional interventions against the decay in clock’s function with age.


Highlights
• Diurnal regulation of polyamine biosynthesis by circadian clock and feeding.
• Polyamine levels regulate the circadian period in cultured cells and mice.
• Polyamines modulate the interaction between the core clock proteins PER2 and CRY1.
• Lengthening of the circadian period with age can be reversed by polyamines.

Conventional analytical size exclusion chromatography (SEC), often used to determine the solution molecular weight of proteins, is subject to inherent limitations and errors. Multi-angle light scattering (MALS) is a first-principles technique for determining the molar mass and size of macromolecules and nanoparticles in solution, independently of conformation. In combination with SEC, MALS overcomes these obstacles to characterize the biophysical properties of proteins and other biomolecules, including molecular weight, size, native oligomeric state, dynamic equilibria and degradation products.

This seminar will present the failure modes of analytical SEC, fundamentals of SEC-MALS and examples of applications to a variety of proteins including IgG, insulin, glycoproteins, membrane proteins and protein complexes as well as viruses and virus-like particles. It will touch on the importance of protein quality control for reproducible science and provide a glimpse into how MALS can analyze complicated protein-protein interactions.

The detection of visual motion is a fundamental neuronal computation that serves many critical behavioral roles, such as encoding of self-motion or figure-ground discrimination. For a neuron to extract directionally selective (DS) motion information from inputs that are not motion selective it is essential to integrate across multiple spatially distinct inputs. This integration step has been studied for decades in both vertebrate and invertebrate visual systems and given rise to several competing computational models. Recent studies in Drosophila have identified the 4th-order neurons, T4 and T5, as the first neurons to show directional selectivity. Due to the small size of these neurons, recordings have been restricted to the use of calcium imaging, limiting timescale and direct measurement of inhibition. These limitations may prevent a clear demonstration of the neuronal computation underlying DS, since it may depend on millisecond-timescale interactions and the integration of excitatory and inhibitory signals. In this study, we use whole cell in-vivo recordings and customized visual stimuli to examine the emergence of DS in T4 cells. We record responses both to a moving bar stimulus and to its components: single position bar flashes. Our results show that T4 cells receive both excitatory and inhibitory inputs, as predicted by a classic circuit model for motion detection. Furthermore, we show that by implementing a passive compartment model of a T4 cell, we can account not only for the DS response of the cell, but also for its dynamics.

Vision is inarguably the most dependable of the five senses. The retina contains light sensing protein receptors (rhodopsins) that incorporate a small polyene molecule derivative of vitamin A, known as 11-cis-retinal. Major clues on understanding the visual cycle have been established through the design of variations of the vitamin A light absorbing molecule, some of which will be presented. A detailed understanding of the inner workings of rhodopsin is not only critical from the stand point of solving mysteries of visual diseases, like Age-related Macular Degeneration (the leading cause of blindness), but also serves as a well established model for elucidating the mechanism of other G-protein coupled receptors (GPCRs). Furthermore, we show that the value of light absorbing molecules expands beyond vision and can be used to trigger neurons thereby aiding the delineation of complex neural networks.