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DTSTART;TZID=America/New_York:20230413T130000
DTEND;TZID=America/New_York:20230413T140000
DTSTAMP:20260731T000805
CREATED:20230824T182821Z
LAST-MODIFIED:20240216T112442Z
UID:10001811-1681390800-1681394400@cmsa.fas.harvard.edu
SUMMARY:Control of actin cable length by decelerated growth and network geometry
DESCRIPTION:Active Matter Seminar\n\n\nSpeaker: Shane McInally\, Brandeis \nTitle: Control of actin cable length by decelerated growth and network geometry \nAbstract: The sizes of many subcellular structures are coordinated with cell size to ensure that these structures meet the functional demands of the cell. In eukaryotic cells\, these subcellular structures are often membrane-bound organelles\, whose volume is the physiologically important aspect of their size. Scaling organelle volume with cell volume can be explained by limiting pool mechanisms\, wherein a constant concentration of molecular building blocks enables subcellular structures to increase in size proportionally with cell volume. However\, limiting pool mechanisms cannot explain how the size of linear subcellular structures\, such as cytoskeletal filaments\, scale with the linear dimensions of the cell. Recently\, we discovered that the length of actin cables in budding yeast (used for intracellular transport) precisely matches the length of the cell in which they are assembled. Using mathematical modeling and quantitative imaging of actin cable growth dynamics\, we found that as the actin cables grow longer\, their extension rates slow (or decelerate)\, enabling cable length to match cell length. Importantly\, this deceleration behavior is cell-length dependent\, allowing cables in longer cells to grow faster\, and therefore reach a longer length before growth stops at the back of the cell. In addition\, we have unexpectedly found that cable length is specified by cable shape. Our imaging analysis reveals that cables progressively taper as they extend from the bud neck into the mother cell\, and further\, this tapering scales with cell length. Integrating observations made for tapering actin networks in other systems\, we have developed a novel mathematical model for cable length control that recapitulates our quantitative experimental observations. Unlike other models of size control\, this model does not require length-dependent rates of assembly or disassembly. Instead\, feedback control over the length of the cable is an emergent property due to the cross-linked and bundled architecture of the actin filaments within the cable. This work reveals a new strategy that cells use to coordinate the size of their internal parts with their linear dimensions. Similar design principles may control the size and scaling of other subcellular structures whose physiologically important dimension is their length.
URL:https://cmsa.fas.harvard.edu/event/am-41323/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Active Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Active-Matter-Seminar-04.13.23.png
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DTSTART;TZID=America/New_York:20230427T130000
DTEND;TZID=America/New_York:20230427T140000
DTSTAMP:20260731T000806
CREATED:20230824T183024Z
LAST-MODIFIED:20240209T052245Z
UID:10001810-1682600400-1682604000@cmsa.fas.harvard.edu
SUMMARY:Competition at the front of expanding populations
DESCRIPTION:Active Matter Seminar\n\n\nSpeaker: Mehran Kardar\, MIT \nTitle: Competition at the front of expanding populations \nAbstract: When competing species grow into new territory\, the population is dominated by descendants of successful ancestors at the expansion front. Successful ancestry depends on the reproductive advantage (fitness)\, as well as ability and opportunity to colonize new domains. (1) Based on symmetry considerations\, we present a model that  integrates both elements by coupling the classic description of one-dimensional competition (Fisher equation) to the minimal model of front shape (KPZ equation). Macroscopic manifestations of these equations on growth morphology are explored\, providing a framework to study spatial competition\, fixation\, and differentiation\, In particular\, we find that ability to expand in space may overcome reproductive advantage in colonizing new territory. (2) Variations of fitness\, as well as fixation time upon differentiation\, are shown to belong to distinct universality classes depending on limits to gain of fitness.
URL:https://cmsa.fas.harvard.edu/event/am-42723/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Active Matter Seminar
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