Research

Physics of living matter


Living systems have evolved intriguing mechanisms of self-regulation to unfold their physical shape and maintain their robust functioning. During development, differentiated cells have to be generated in the right number and sequence; during adult life, stem cells and specialised cells have to coordinate their activity and proliferation cycles in order to maintain the function of organs and repair injuries.

In all these different contexts, the robust collective behaviour of cell populations relies on their capacity to self-regulate, which emerges from the interplay between local cellular operations and intercellular coupling. When this interplay is compromised, diseases can arise.

In many cases, cells and their surrounding tissues constitute a homeostatic ‘ecosystem’ that can be described in terms of niche interactions, cellular diversity, adaptation, collaboration, selective advantage and competition for resources. How do such ecological principles shape the collective behaviour of cell populations within organisms and ensure their correct development, homeostasis and coordination in a self-organised way? And how do diseased tissues such as tumours exploit interactions with their healthy environment to hijack self-regulatory mechanisms and form their own niche environments?

Developmental pattern formation

Using methods from non-equilibrium physics, I study the collective regulation of timing and morphologies during embryonic patterning, in particulat during vertebrate segmentation and neurogenesis.

Stem cell dynamics

Using methods from statistical physics and dynamical systems theory, I investigate how stem cells maintain adult tissue and lead to recovery of tissue after injury. Moreover, I study how the stem cell pool size is regulated by intercellular signaling.

Selected publications
  1. The proneural wave in the Drosophila optic lobe is driven by an excitable reaction-diffusion mechanism
    Jörg et al., eLife 8, e40919 (2019)
  2. Faster embryonic segmentation through elevated Delta-Notch signalling
    Liao et al., Nature Commun. 7, 11861 (2016)
  3. Continuum theory of gene expression waves during vertebrate segmentation
    Jörg et al., New J. Phys. 17, 093042 (2015)
  4. A Doppler effect in embryonic pattern formation
    Soroldoni et al., Science 345, 222—225 (2014)

Selected publications
  1. Stem cell populations as self-renewing many-particle systems
    Jörg et al., Annu. Rev. Condens. Matter Phys. 12, 135–153 (2021)
  2. Competition for mitogens regulates spermatogenic stem cell homeostasis in an open niche
    Kitadate et al., Cell Stem Cell 24, 79–92 (2019)
  3. Live imaging of neurogenesis in the adult mouse hippocampus
    Pilz et al., Science 359, 658–662 (2018)
  4. Fate mapping of human glioblastoma reveals an invariant stem cell hierarchy
    Lan et al., Nature 549, 227 (2017)

Nonlinear dynamics


Limit cycles and coupled oscillators

Oscillators often tend to synchronise in the presence of coupling. Depending on the features of oscillators and coupling, the system can exhibit intriguing and counterintuitive transient dynamics.

I study the spatiotemporal phase patterns that occur during these transient dynamics and how they depend on the properties of the coupled system. In particular, I focus on the role of inert signal propagation and processing, i.e., time delays in the oscillator coupling and slow frequency adaptation of individual oscillators.

Electronic synchronisation

Electronic components that perform tasks in a concerted way rely on a common time reference. We developed a novel approach to achieve such a common time reference in large systems by synchronising a distributed network of electronic oscillators.

Instead of a traditional master-clock approach, in which one master oscillator entrains nodes, our approach exploits the self-organised synchronisation of mutually delay-coupled oscillators.

This project lives on, headed by Dr Lucas Wetzel:
“Chronoloom”

Selected publications
  1. Stochastic Kuramoto oscillators with discrete phase states
    Jörg, Phys. Rev. E 96, 032201 (2017)
  2. Amplitude bounds for biochemical oscillators
    Jörg, Europhys. Lett. 119, 58004 (2017)
  3. Synchronization dynamics in the presence of coupling delays and phase shifts
    Jörg et al., Phys. Rev. Lett. 112, 174101 (2014)
  4. Collective modes of coupled phase oscillators with delayed coupling
    Ares et al., Phys. Rev. Lett. 108, 204101 (2012)

Selected publications
  1. Self-organized synchronization of digital phase-locked loops with delayed coupling in theory and experiment
    Wetzel et al., PLOS ONE 12, e0171590 (2017)
  2. Synchronization in networks of mutually delay-coupled phase-locked loops
    Pollakis et al., New J. Phys. 16, 113009 (2014)
  3. Self-synchronizable Network
    Pollakis et al., 2957982 B1 (2017)

Overview

Theoretical Biology Theoretical Physics
Stem cell fate dynamics
  • Adult neurogenesis
  • Germ line maintenance
  • Stomach gland homeostasis
  • Cancer stem cells
Morphogenesis and developmental pattern formation
  • Somitogenesis
  • Neurogenesis
  • Genetic oscillations
  • Biochemical signal transduction
Non-equilibrium and statistical physics
  • Active matter
  • Population dynamics
Nonlinear and stochastic dynamics
  • Coupled oscillators
  • Nonlinear time series analysis
Electronic synchronisation technologies
  • Self-organised synchronisation of digital clocks