Sujit Kumar Nath

Biophysical Modelling of Morphogenesis and Growth in Plant and Animal Systems

The emergence of forms in living systems arises from the interplay of biochemical signalling and physical forces. In this talk, I will present a biophysical perspective on growth and shape regulation across plant and animal systems, combining theory, modelling, and experiments.

I will first discuss plant root gravitropism, addressing how roots sense gravity and translate this into directed growth. By integrating high-throughput experiments with theory, we develop a compact model that couples tip-based sensing, signal transduction, and biomechanical response. This sensing-growth feedback framework quantitatively captures both transient and long-term bending dynamics across a wide range of conditions, and reveals the interplay of sensing, signalling, and mechanics across overlapping timescales. We demonstrate our results in the mean-field to capture population dynamics as well as in a stochastic individual root setting.

I will then turn to cell competition in animal epithelia, where tissue homeostasis emerges from mechanical interactions between cell populations with differing mechanosensitivities. Motivated by experiments on wild-type and pressure-immune mutant epithelial cells, we develop a continuum active-matter model in which tissue composition and cell density evolve under active stresses, mechanical pressure, and pressure-dependent cell death. Differences in mechanosensitivity generate a self-reinforcing feedback: elevated mutant fraction increases active stress, raising tissue pressure, which selectively drives cell death in wild-type cells. The coupled nonlinear PDE system identifies critical parameters governing transitions between coexistence, wild-type dominance, and mutant dominance, offering a mechanistic basis for stress-driven competitive exclusion in crowded epithelia and cancer growth.

Together, these studies underscore common physical principles-feedback, transport, and mechanics that drive the emergence of forms and shapes across biological systems.