The dorsal morphogen gradient regulates the mesoderm determinant twist in early Drosophila embryos.
A gradient of the maternal morphogen dorsal (dl) initiates the differentiation of various tissues along the dorsal-ventral axis of early Drosophila embryos. dl is a sequence-specific DNA-binding protein that is related to the mammalian regulatory factor NF-kappa B. Previous studies suggest that dl can function as a transcriptional repressor. To determine how dl functions as an activator we have examined the promoter of the mesoderm determinant gene twist (twi). Genetic studies suggest that peak levels of dl protein in ventral regions of early embryos initiate twi expression. Using a combination of promoter fusion-P-transformation assays, and in vitro DNA-binding assays coupled with site-directed mutagenesis, we establish a direct link between dl-binding sites and twi expression in the early embryo. We also present evidence that the dorsal-ventral limits of twi expression depend on the number and affinity of dl-binding sites present in its promoter. A comparison of twi with a second dl target gene, zen, suggests a correlation between the affinities of dl-binding sites and response to different thresholds of dl morphogen.
Jiang
J
J
Department of Biological Sciences, Columbia University, New York, New York 10027.
Kosman
D
D
Ip
Y T
YT
Levine
M
M
D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D003850:Deoxyribonuclease I; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D029721:Drosophila Proteins; D004625:Embryo, Nonmammalian / Q000502:physiology*; D005246:Feedback; D008648:Mesoderm / Q000502:physiology; D008969:Molecular Sequence Data; D009024:Morphogenesis; D016297:Mutagenesis, Site-Directed; D016328:NF-kappa B / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D015345:Oligonucleotide Probes; D010750:Phosphoproteins; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D016328:NF-kappa B; D009687:Nuclear Proteins; D015345:Oligonucleotide Probes; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C062236:dl protein, Drosophila; D004247:DNA; D003850:Deoxyribonuclease I; D001616:beta-Galactosidase