Upcoming Seminars / Seminars This Week

Wed 4/8/20 12 noon
Mathematical Biology Seminar
Daniel Cooney (Princeton University)
PDE Models of Multilevel Selection: The Evolution of Cooperation and the Shadow of Individual Selection
Here we consider a game theoretic model of multilevel selection in which individuals compete based on their payoff and groups also compete based on the average payoff of group members. Our focus is on the Prisoners' Dilemma: a game in which individuals are best off cheating, while groups of individuals do best when composed of many cooperators. We analyze the dynamics of the two-level replicator dynamics, a nonlocal hyperbolic PDE describing deterministic birth-death dynamics for both individuals and groups. Comparison principles and an invariant property of the tail of the population distribution are used to characterize the threshold level of between-group selection dividing a regime in which the population converges to a delta function at the equilibrium of the within-group dynamics from a regime in which between-group competition facilitates the existence of steady-state densities supporting greater levels of cooperation. In particular, we see that the threshold selection strength and average payoff at steady state depend on a tug-of-war between the individual-level incentive to be a defector in a many-cooperator group and the group-level incentive to have many cooperators over many defectors. We also find that lower-level selection casts a long shadow: if groups are best off with a mix of cooperators and defectors, then there will always be fewer cooperators than optimal at steady state, even in the limit of infinitely strong competition between groups.
Hosted by Profs.Jonathan Touboul and Thomas Fai, and Dr. Youngmin Park

Thu 4/9/20 4 pmOnline
MRSEC Seminar
Ben Rogers (Brandeis University)
Nucleation and growth of DNA-programmed crystallization
Grafting DNA onto microscopic colloidal particles can `program' them with information that tells them exactly how to self-assemble. Recent advances in our understanding of the specific interactions that emerge due to DNA hybridization have enabled the assembly of a wide variety of crystal structures. However, the dynamic pathways by which these crystals self-assemble are largely unknown. In this talk I will present an experimental study of the nucleation and growth kinetics of colloidal crystallization due to DNA hybridization. Specifically, I will describe a microfluidics-based approach in which we produce hundreds of monodisperse, isolated droplets filled with colloidal particles and then track the formation of crystals within each drop as a function of time. We find that the initial nucleation of crystals from a supersaturated solution involves overcoming a free-energy barrier, whose height depends strongly on temperature and can be described using classical nucleation theory. We also find that once nucleated, colloidal crystals grow at a rate that is limited by the diffusive flux of colloidal particles to the growing crystal surface. Taken together, these two findings quantitatively describe the full dynamic pathway leading from the initial disordered fluid to the final ordered solid. We anticipate that our results will yield new protocols for making higher quality or more complex self-assembled structures by controlling the dynamics of their assembly.
Hosted by John Berezney

Mon 4/13/20 12 noonOnline
Neurobiology Journal Club
Abuzar Mahmood (Katz Lab)
Motor cortex signals for each arm are mixed across hemispheres and neurons yet partitioned within the population response
Juliet Bottorff (Turrigiano Lab)
Noradrenergic signaling in the wakeful state inhibits microglial surveillance and synaptic plasticity in the mouse visual cortex

Thu 4/16/20 4 pmOnline
MRSEC Seminar
Peter Foster (MIT)
From Cytoskeletal Assemblies to Living Machines
The cytoskeleton has the remarkable ability to self-organize into living machines which underlie diverse cellular processes. These nonequilibrium machines are driven by molecular motor proteins which shape cytoskeletal components into soft active materials. How the properties of these materials emerge from protein-level interactions and energetics is an open question. Here, I'll present work on the dynamics, mechanics, and energetics of microtubule/motor protein networks. In cell extracts, we've found that microtubule networks undergo a spontaneous bulk contraction driven by the motor protein dynein, which can be quantitatively understood using an active fluid model coarse-grained from motor-scale interactions. Additionally, we've used picowatt calorimetry to measure the heat dissipated by an active cytoskeletal material composed of purified components and found that the efficiency for generating large-scale flows is remarkably low. Taken together, these results uncover design principles for building active materials and represent a step towards building a thermodynamic understanding of active matter.
Hosted by John Berezney

Fri 4/17/20 11:15 amRosenstiel 118
Biochemistry-Biophysics Friday Lunchtime Pizza Talks
Debora Marks (Harvard Medical School)
Event Cancelled
Learning the Secrets of Sequences with Deep Generative Models
Hosted by Niels Bradshaw

Mon 4/20/20 12 noonOnline
Neurobiology Journal Club
Aishwarya Krishnamoorthy (Kadener Lab)
Drosophila insulin-like peptide 2 mediates dietary regulation of sleep intensity
Susannah Slepian (Paradis Lab)

Tue 4/21/20 12:30 pmGerstenzang 121
Joint Biology/Neuroscience Colloquium
Nilay Yapici (Cornell)
Hosted by Leslie Griffith and Don Katz

Thu 4/23/20 10 am
Special Seminar
Biochemistry students
Annual Senior Thesis and Masters Thesis Talks

Thu 4/23/20 11 amVolen 201
Computational Neuroscience Journal Club
Samuel Gershman (Harvard)
Predictive maps in the brain
Pizza will be served.
Hosted by Jordan Breffle

Thu 4/23/20 4:30 pmGoldsmith 317
Joint Mathematics Colloquium
Margaret Beck (Boston University)
Hosted by Prof. Daniel Ruberman

Fri 4/24/20 2 pm
Special Seminar
Biochemistry students
Annual Senior Thesis and Masters Thesis Talks

Mon 4/27/20 12 noonOnline
Neurobiology Journal Club
Rabia Anjum (Paradis Lab)
Daniel Svedberg (Katz Lab)

Tue 4/28/20 12:30 pmGerstenzang 121
Joint Biology/Neuroscience Colloquium (Lisman Memorial Lecture in Vision Science)
Doris Tsao (California Institute of Technology)
POSTPONED until 2020-2021 academic year
"How the brain represents objects"
Hosted by Steve Van Hooser

Tue 5/5/20 12:30 pmOnline
Joint Biology/Neuroscience Colloquium
Nevan Krogan (UCSF)
Hosted by Jim Haber

Thu 5/7/20 4 pmOnline
MRSEC Seminar
Alexandre Bisson (Brandeis University, Biology)
Hosted by John Berezney

Fri 5/8/20 11:15 amRosenstiel 118
Biochemistry-Biophysics Friday Lunchtime Pizza Talks
Wilfred van der Donk (University of Illinois at Urbana-Champaign)
Event Cancelled
Natural Product Biosynthesis by Posttranslational Modification
Hosted by Daniel Oprian

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