3 minutes to precisely measure morphogen concentration

PLoS Genet. 2018 Oct 26;14(10):e1007676. doi: 10.1371/journal.pgen.1007676. eCollection 2018 Oct.


Morphogen gradients provide concentration-dependent positional information along polarity axes. Although the dynamics of the establishment of these gradients is well described, precision and noise in the downstream activation processes remain elusive. A simple paradigm to address these questions is the Bicoid morphogen gradient that elicits a rapid step-like transcriptional response in young fruit fly embryos. Focusing on the expression of the major Bicoid target, hunchback (hb), at the onset of zygotic transcription, we used the MS2-MCP approach which combines fluorescent labeling of nascent mRNA with live imaging at high spatial and temporal resolution. Removing 36 putative Zelda binding sites unexpectedly present in the original MS2 reporter, we show that the 750 bp of the hb promoter are sufficient to recapitulate endogenous expression at the onset of zygotic transcription. After each mitosis, in the anterior, expression is turned on to rapidly reach a plateau with all nuclei expressing the reporter. Consistent with a Bicoid dose-dependent activation process, the time period required to reach the plateau increases with the distance to the anterior pole. Despite the challenge imposed by frequent mitoses and high nuclei-to-nuclei variability in transcription kinetics, it only takes 3 minutes at each interphase for the MS2 reporter loci to distinguish subtle differences in Bicoid concentration and establish a steadily positioned and steep (Hill coefficient ~ 7) expression boundary. Modeling based on the cooperativity between the 6 known Bicoid binding sites in the hb promoter region, assuming rate limiting concentrations of the Bicoid transcription factor at the boundary, is able to capture the observed dynamics of pattern establishment but not the steepness of the boundary. This suggests that a simple model based only on the cooperative binding of Bicoid is not sufficient to describe the spatiotemporal dynamics of early hb expression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites / genetics
  • Body Patterning / genetics
  • DNA-Binding Proteins / genetics
  • Drosophila Proteins / genetics
  • Drosophila melanogaster / embryology*
  • Drosophila melanogaster / genetics
  • Embryo, Nonmammalian / metabolism
  • Gene Expression Regulation, Developmental / genetics
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / physiology*
  • Morphogenesis / physiology*
  • Optical Imaging / methods
  • Promoter Regions, Genetic / genetics
  • Trans-Activators / genetics
  • Trans-Activators / physiology*
  • Transcription Factors / genetics
  • Zygote / metabolism


  • DNA-Binding Proteins
  • Drosophila Proteins
  • Homeodomain Proteins
  • Trans-Activators
  • Transcription Factors
  • bcd protein, Drosophila
  • hb protein, Drosophila

Grant support

This work was supported by a PSL IDEX REFLEX Grant for Mesoscopic Biology (ND, AMW, MC), ANR- 11-BSV2-0024 Axomorph (ND and AMW), ARC PJA20151203341 (ND), ANR-11-LABX-0044 DEEP Labex (ND), an Ontario Trillium Scholarship for International Students (CAPR), a Mitacs Global Link Scholarship (CAPR) and an Internal Curie Institute Scholarship (CAPR), a Mayent Rothschild sabbatical Grant from the Curie Institute (CF) and an NSERC discovery grant RGPIN/06362-15 (CF), a Marie Curie MCCIG grant No. 303561 (AMW) and PSL ANR-10-IDEX-0001-02. - https://www.psl.eu/en/research/funding-opportunities/psl-calls-proposals - http://www.agence-nationale-recherche.fr/en/ - https://www.fondation-arc.org/espace-chercheur - https://grad.uwo.ca/current_students/student_finances/ots.html - https://www.mitacs.ca/en/programs/globalink - https://enseignement.curie.fr/en/content/senior-researcher-sabbatical - http://www.nserc-crsng.gc.ca/index_eng.asp -https://ec.europa.eu/research/participants/portal/desktop/en/opportunities/fp7/calls/fp7-people-2013-cig.html The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.