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.
Active Forces and Flows that Pattern Organisms by Stephan Grill
International Centre for Theoretical Sciences via YouTube
Overview
Syllabus
Stephan Grill
Active Forces and Flows that Pattern Organisms
'Morphogenesis' - generation of form
From the molecular to the mesoscale
Difficult problem.
Specific Questions:
A key molecule
Actin and myosin
Thin actomyosin cortical layer
The cortex is an active material
Behaviour at larger scales
The cell cortex in the C. elegant zygote
Actomyosin cortical flow
Flow polarizes the C. elegant zygote
Active surface drive cytosolic flows
Large length- and time scales Continuum description
Elastic on short times
Force balance between active and passive forces
Theory: Thin film of an active gel
Everything takes place within a thin film
Thin film active viscous fluid theory describes cortical flow in in zebrafish
Active tension gradients drives flow
Active tension gradients drives flow Flows drive zebrafish epiboly
Shear and compression in cortical flow aligns action filaments
Cortical flow aligns action filaments to form a cytokinesic ingression
The cortex generates torques of defined handedness.
Chiral rotating flow
Chirality and L/R symmetry breaking
In higher vertebrates,
The cell cortex has been implied to play a role in instances of left/right symmetry breaking
How does chiral flow come about?
Generic theory for active chiral fluids
Thin film active chiral fluid
The cortex actively generates torques of defined handedness
Is myosin activity responsible for active torque generation?
RNAi of mic-4
Modulating myosin activity
Modulating myosin activity affects chiral flow
Myosin activity is required for generating active torques.
Hypothesis: mic-4 RNAi reduces active tension and active torque proportionally
11 hours of mic-4 RNAi reduces active torque more than active tension
Weak perturbation RNAi
Chiral counterrotation velocity Vc
Weak perturbation mic-4 RNAi
Can we change the torque?
Weak perturbation RNAi of Rho signaling
A mild change in Rho signaling modulates active torques.
C. elegansahody axis establishment
Counterrotatory flows in ABa
Proposed mechanism:
Does the chiral skew of ABa and ABp change when we modify active torque generation?
Active torques execute left/right body axis establishment in C. elegans
Mesoscale 'active matter' properties
Mechanochemically pattern formation
Thin film active fluid with regulator
Pulsatory patterns in actomyosin systems are ubiquitous
Active pulsatory patterns daCA, I = -nozu + yu OLA = DAOZA - Ox VA
Pulsatory patterns with differential turnover Force balance: OxCA, I = -nozu + yu
Active matter and regulation
Entrainment tunes a mechanochemically unstable pattern to small spatial wavelengths
What about PAR polarization?
Peter Vijay Gross Krishamurthy
PAR proteins are transported by flow
Mechanochemically feedback drives PAR polarization
PAR polarization: Theory and Experiment
Spatiotemporal evolution of polarization, theory
Pattern Formation
Suggestion:
Fast turn-over up-regulator
Actomyosin regulation
Taught by
International Centre for Theoretical Sciences
