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Stephan Grill
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Active Forces and Flows that Pattern Organisms
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'Morphogenesis' - generation of form
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From the molecular to the mesoscale
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Difficult problem.
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Specific Questions:
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A key molecule
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Actin and myosin
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Thin actomyosin cortical layer
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The cortex is an active material
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Behaviour at larger scales
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The cell cortex in the C. elegant zygote
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Actomyosin cortical flow
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Flow polarizes the C. elegant zygote
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Active surface drive cytosolic flows
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Large length- and time scales Continuum description
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Elastic on short times
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Force balance between active and passive forces
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Theory: Thin film of an active gel
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Everything takes place within a thin film
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Thin film active viscous fluid theory describes cortical flow in in zebrafish
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Active tension gradients drives flow
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Active tension gradients drives flow Flows drive zebrafish epiboly
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Shear and compression in cortical flow aligns action filaments
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Cortical flow aligns action filaments to form a cytokinesic ingression
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The cortex generates torques of defined handedness.
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Chiral rotating flow
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Chirality and L/R symmetry breaking
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In higher vertebrates,
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The cell cortex has been implied to play a role in instances of left/right symmetry breaking
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How does chiral flow come about?
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Generic theory for active chiral fluids
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Thin film active chiral fluid
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The cortex actively generates torques of defined handedness
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Is myosin activity responsible for active torque generation?
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RNAi of mic-4
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Modulating myosin activity
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Modulating myosin activity affects chiral flow
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Myosin activity is required for generating active torques.
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Hypothesis: mic-4 RNAi reduces active tension and active torque proportionally
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11 hours of mic-4 RNAi reduces active torque more than active tension
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Weak perturbation RNAi
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Chiral counterrotation velocity Vc
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Weak perturbation mic-4 RNAi
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Can we change the torque?
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Weak perturbation RNAi of Rho signaling
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A mild change in Rho signaling modulates active torques.
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C. elegansahody axis establishment
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Counterrotatory flows in ABa
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Proposed mechanism:
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Does the chiral skew of ABa and ABp change when we modify active torque generation?
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Active torques execute left/right body axis establishment in C. elegans
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Mesoscale 'active matter' properties
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Mechanochemically pattern formation
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Thin film active fluid with regulator
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Pulsatory patterns in actomyosin systems are ubiquitous
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Active pulsatory patterns daCA, I = -nozu + yu OLA = DAOZA - Ox VA
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Pulsatory patterns with differential turnover Force balance: OxCA, I = -nozu + yu
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Active matter and regulation
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Entrainment tunes a mechanochemically unstable pattern to small spatial wavelengths
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What about PAR polarization?
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Peter Vijay Gross Krishamurthy
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PAR proteins are transported by flow
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Mechanochemically feedback drives PAR polarization
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PAR polarization: Theory and Experiment
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Spatiotemporal evolution of polarization, theory
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Pattern Formation
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Suggestion:
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Fast turn-over up-regulator
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Actomyosin regulation
Description:
Explore the intricate world of biological self-organization in this comprehensive lecture on active forces and flows that pattern organisms. Delve into the complex processes of morphogenesis, from molecular to mesoscale levels, with a focus on the actomyosin cortical layer and its role in cellular dynamics. Examine how active tension gradients drive cortical flows in various organisms, including C. elegans and zebrafish. Investigate the generation of chiral rotating flows and their implications for left-right symmetry breaking in higher vertebrates. Analyze the role of myosin activity in generating active torques and its impact on body axis establishment. Discover mechanochemical pattern formation in active fluids and explore the concept of entrainment in tuning unstable patterns. Gain insights into PAR protein polarization and its relationship to cortical flows. Throughout the lecture, encounter theoretical models and experimental evidence that illuminate the fascinating interplay between active forces, flows, and biological patterning. Read more

Active Forces and Flows that Pattern Organisms by Stephan Grill

International Centre for Theoretical Sciences
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#Science #Biology #Developmental Biology #Morphogenesis
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Stephan Grill