Phosphorylation of Bicoid on MAP-kinase sites: Contribution to its interaction with the torso pathway

Florence Janody, Rachel Sturny, Françoise Catala, Claude Desplan, Nathalie Dostatni

Research output: Contribution to journalArticlepeer-review

Abstract

The Torso signal transduction pathway exhibits opposite effects on the activity of the Bicoid (Bcd) morphogen: (i) Bcd function is repressed by Torso (Tor) at the anterior pole of the embryo leading to a retraction of the expression of many Bcd targets from the most anterior region of the embryo, where the Tor tyrosine kinase receptor is activated, and (ii) Bcd function is strengthened by Tor in a broader anterior region, as indicated by a shift of the posterior herder of Bcd targets towards the anterior pole in embryos deprived from Tor activity. Anterior repression of Bcd targets was not observed in embryos lacking maternal contribution of D-sor, which acts downstream of Tor and encodes a MAP-kinase kinase. This indicates that the Ras signalling cascade is directly involved in this process, although the known transcriptional effecters of the Tor pathway, tll and hkb, are not. Bcd is a good in vitro substrate for phosphorylation by MAP-kinase and phosphorylation of the protein occur in vivo on MAP-kinase sites. In the presence of a Bcd mutant that could no longer be phosphorylated by MAP-kinase, expression of Bcd targets remained repressed by Tor at the pole while strengthening of Bcd activity was reduced. These experiments indicate that phosphorylation of Bcd by MAP-kinase is likely to be required for the Tor pathway to induce its full positive effect on Bcd. This suggests that Tor signalling acts at a distance from the anterior pole by direct modification of the diffusing Bcd morphogen.

Original languageEnglish (US)
Pages (from-to)279-289
Number of pages11
JournalDevelopment
Volume127
Issue number2
StatePublished - Jan 2000

Keywords

  • Bcd
  • Drosophila
  • MAP-kinase
  • Phosphorylation
  • Torso

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology

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