# Hunchback promoters can readout morphogenetic positional information in less than a minute

## TL;DR

This paper demonstrates that hunchback gene promoters can rapidly interpret Bicoid morphogen signals within a minute, using efficient decision strategies and specific promoter architectures, challenging traditional fixed-time sampling assumptions.

## Contribution

It introduces on-the-fly decision models and identifies promoter architectures enabling fast, accurate morphogen readout in early fly embryogenesis.

## Key findings

- Fast decision schemes outperform fixed-time sampling in speed and accuracy.
- Specific promoter architectures facilitate rapid and reliable positional information readout.
- Predictions for Bicoid mutant experiments are formulated.

## Abstract

The first cell fate decisions in the developing fly embryo are made very rapidly : hunchback genes decide in a few minutes whether a given nucleus follows the anterior or the posterior developmental blueprint by reading out the positional information encoded in the Bicoid morphogen. This developmental system constitutes a prototypical instance of the broad spectrum of regulatory decision processes that combine speed and accuracy. Traditional arguments based on fixed-time sampling of Bicoid concentration indicate that an accurate readout is not possible within the short times observed experimentally. This raises the general issue of how speed-accuracy tradeoffs are achieved. Here, we compare fixed-time sampling strategies to decisions made on-the-fly, which are based on updating and comparing the likelihoods of being at an anterior or a posterior location. We found that these more efficient schemes can complete reliable cell fate decisions even within the very short embryological timescales. We discuss the influence of promoter architectures on the mean decision time and decision error rate and present concrete promoter architectures that allow for the fast readout of the morphogen. Lastly, we formulate explicit predictions for new experiments involving Bicoid mutants.