TY - JOUR
T1 - Neither the homeodomain nor the activation domain of Bicoid is specifically required for its down-regulation by the Torso receptor tyrosine kinase cascade
AU - Bellaïche, Yohanns
AU - Bandyopadhyay, Rupa
AU - Desplan, Claude
AU - Dostatni, Nathalie
PY - 1996
Y1 - 1996
N2 - Bicoid (Bcd) is a maternal morphogen responsible for patterning the head and thorax of the Drosophila embryo. Correct specification of head structure, however, requires the activity of the Torso receptor tyrosine kinase cascade, which also represses expression of Bcd targets at the most anterior tip of the embryo. Here, we investigate the role of both the homeodomain (HD) and the activation domain of Bcd in the anterior repression of its targets. When a Bcd mutant protein whose HD has been replaced by the Gal4 DNA-binding domain is expressed in early embryos, a reporter gene driven by Gal4 DNA-binding sites is first activated in an anterior domain and then repressed from the anterior pole. The down-regulation of Bcd-Gal4 activity requires torso function but does not depend on endogenous bcd activity, indicating that the Bcd protein alone and none of its targets is required to mediate the effect of torso. Functional analysis of a chimeric protein, whose activation domain has been replaced by a generic activation domain, indicates that the activation domain of Bcd is also not specifically required for its downregulation by Torso. We propose that Torso does not affect the ability of Bcd to bind DNA, but instead directs modification of Bcd or of a potential Bcd co-factor, which renders the Bcd protein unable to activate transcription.
AB - Bicoid (Bcd) is a maternal morphogen responsible for patterning the head and thorax of the Drosophila embryo. Correct specification of head structure, however, requires the activity of the Torso receptor tyrosine kinase cascade, which also represses expression of Bcd targets at the most anterior tip of the embryo. Here, we investigate the role of both the homeodomain (HD) and the activation domain of Bcd in the anterior repression of its targets. When a Bcd mutant protein whose HD has been replaced by the Gal4 DNA-binding domain is expressed in early embryos, a reporter gene driven by Gal4 DNA-binding sites is first activated in an anterior domain and then repressed from the anterior pole. The down-regulation of Bcd-Gal4 activity requires torso function but does not depend on endogenous bcd activity, indicating that the Bcd protein alone and none of its targets is required to mediate the effect of torso. Functional analysis of a chimeric protein, whose activation domain has been replaced by a generic activation domain, indicates that the activation domain of Bcd is also not specifically required for its downregulation by Torso. We propose that Torso does not affect the ability of Bcd to bind DNA, but instead directs modification of Bcd or of a potential Bcd co-factor, which renders the Bcd protein unable to activate transcription.
KW - Bicoid
KW - Drosophila
KW - RTK signal transduction cascade
KW - Transcription
UR - http://www.scopus.com/inward/record.url?scp=0029855382&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0029855382&partnerID=8YFLogxK
M3 - Article
C2 - 8951065
AN - SCOPUS:0029855382
SN - 0950-1991
VL - 122
SP - 3499
EP - 3508
JO - Development
JF - Development
IS - 11
ER -