Interference between the PHA-4 and PEB-1 transcription factors in formation of the Caenorhabditis elegans pharynx.
PHA-4 is a forkhead/winged helix transcription factor that acts as an organ identity factor in the development of the Caenorhabditis elegans pharynx. PEB-1 is a novel DNA-binding protein also involved in pharyngeal morphogenesis. PHA-4 and PEB-1 bind at overlapping sites on the C183 sequence element that controls pharynx-specific expression of the C. elegans myo-2 gene. It has been suggested that PHA-4 and PEB-1 act cooperatively on the C183 sequence. In this study, we test this model and assess the C183-dependent transcriptional activity of PHA-4 and PEB-1, both individually and in combination. We show that PHA-4 and PEB-1 are both modest transcriptional activators in yeast but that co-expression of the two factors does not result in significantly increased expression of a C183-regulated reporter gene. Electrophoretic mobility-shift assays provide no evidence for the formation of a PHA-4/PEB-1 complex in vitro but rather show that PHA-4 and PEB-1 cannot bind C183 simultaneously. As we have reported previously, ectopic expression of PHA-4 in C. elegans causes ectopic expression of a C183-regulated reporter gene. We show that ectopic expression of PEB-1 cannot cause ectopic expression of the same reporter but rather ectopic PEB-1 inhibits reporter gene activation by PHA-4. Overall, our results do not support a model in which PHA-4 and PEB-1 synergize in vivo but rather support a model in which PEB-1 may negatively modulate PHA-4's ability to activate transcription through C183 during formation of the C. elegans pharynx.
Kalb
John M
JM
Department of Biochemistry and Molecular Biology, Genes and Development Research Group, Faculty of Medicine, Health Sciences Centre, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1.
Beaster-Jones
Laura
L
Fernandez
Anthony P
AP
Okkema
Peter G
PG
Goszczynski
Barbara
B
McGhee
James D
JD
D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology / Q000235:genetics / Q000502:physiology; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D010614:Pharynx / Q000196:embryology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D012441:Saccharomyces cerevisiae; D024745:Smooth Muscle Myosins / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D029742:Caenorhabditis elegans Proteins; D004268:DNA-Binding Proteins; C113277:Pha-4 protein, C elegans; D020033:Protein Isoforms; D015534:Trans-Activators; C420182:peb-1 protein, C elegans; D024745:Smooth Muscle Myosins