Interpretation of morphogen gradients by a synthetic bistable circuit

Paul K Grant,Valerie Coppard,Gregory Szep,James C W Locke,Jim Haseloff,Andrew Phillips,Attila Csikász-Nagy,Neil Dalchau,Om Patange,Jacob Halatek

doi:10.1038/s41467-020-19098-w

Abstract

During development, cells gain positional information through the interpretation of dynamic morphogen gradients. A proposed mechanism for interpreting opposing morphogen gradients is mutual inhibition of downstream transcription factors, but isolating the role of this specific motif within a natural network remains a challenge. Here, we engineer a synthetic morphogen-induced mutual inhibition circuit in E. coli populations and show that mutual inhibition alone is sufficient to produce stable domains of gene expression in response to dynamic morphogen gradients, provided the spatial average of the morphogens falls within the region of bistability at the single cell level. When we add sender devices, the resulting patterning circuit produces theoretically predicted self-organised gene expression domains in response to a single gradient. We develop computational models of our synthetic circuits parameterised to timecourse fluorescence data, providing both a theoretical and experimental framework for engineering morphogen-induced spatial patterning in cell populations.

Highlights

During development, cells gain positional information through the interpretation of dynamic morphogen gradients
By taking a synthetic biology approach[20,21,22,23] we have built a morphogen-induced mutual inhibition circuit from scratch that acts in isolation in E. coli and used it to investigate the conditions under which patterning occurs
To investigate whether a simple mutual inhibition network topology can interpret dynamic gradients, we built a synthetic Exclusive Receiver circuit (Fig. 1c), based on a previous Receiver circuit design that responds to two homoserine lactone (HSL) input signals, 3O-C6-HSL (C6) and 3O-C12-HSL (C12) with fluorescent protein outputs

Summary

Introduction

Cells gain positional information through the interpretation of dynamic morphogen gradients. We engineer a synthetic morphogen-induced mutual inhibition circuit in E. coli populations and show that mutual inhibition alone is sufficient to produce stable domains of gene expression in response to dynamic morphogen gradients, provided the spatial average of the morphogens falls within the region of bistability at the single cell level. We develop computational models of our synthetic circuits parameterised to timecourse fluorescence data, providing both a theoretical and experimental framework for engineering morphogen-induced spatial patterning in cell populations. 1234567890():,; The positional information solution to the French flag problem, in which cells compute their spatial position by responding to the concentration of a morphogen in a gradient[1], provides crucial insight into how patterns of gene expression form in a developing organism. We show that the mutual inhibition motif[19] is sufficient to produce stable domains of gene expression in response to dynamic and transient morphogen gradients. The experimental control and precise measurement afforded by a synthetic biology framework allowed us to understand the behaviour of these patterning mechanisms at a quantitative level in the context of a mathematical model parameterized against data, and to uncover general design principles for engineering multicellular systems

Methods

Results

Conclusion