A mechanism for hunchback promoters to readout morphogenetic positional information in less than a minute

Abstract

Cell fate decisions in the y embryo are rapid: hunchback genes decide in minutes whether nuclei follow the anterior/posterior developmental blueprint by reading out positional information in the Bicoid morphogen. This developmental system is a prototype of regulatory decision processes that combine speed and accuracy. Traditional arguments based on xed-time sampling of Bicoid concentration indicate that an accurate readout is impossible within the experimental times. This raises the general issue of how speed-accuracy tradeo s are achieved. Here, we compare xed-time to on-the-y decisions, based on comparing the likelihoods of anterior/posterior locations. We found that these more e cient schemes complete reliable cell fate decisions within the short embryological timescales. We discuss the in uence of promoter architectures on decision times and error rates, present concrete examples that rapidly readout the morphogen, and predictions for new experiments. Lastly, we suggest a simple mechanism for RNA production and degradation that approximates the log-likelihood function.