How does the fushi tarazu gene activate engrailed in the Drosophila embryo?
In the even-numbered parasegments of the Drosophila embryo, expression of the fushi tarazu (ftz) gene is necessary for transcription of engrailed (en). Yet those cells expressing ftz+ in a stripe, only the anteriormost come to express en. One explanation is that the level of ftz+ might be graded across the stripe and in order to express en, it would be sufficient for cells to exceed a threshold concentration of Ftz protein. We use photographs and microspectrophotometry to measure differences in Ftz antigen concentration; we do not find a gradient within the Ftz stripe. Rather, the stripe appears to contain cells with similar amounts of antigen plus a few weakly staining cells that are usually at the posterior edge. Further, varying the amount of Ftz protein has no effect on en expression. Finally, embryos lacking the even-skipped gene have normal levels of Ftz but do not express en. Our observations appear to rule out the threshold hypothesis.
MRC Laboratory of Molecular Biology, Cambridge, UK.
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D000818:Animals; D030801:Animals, Genetically Modified; D019521:Body Patterning / Q000235:genetics*; D004251:DNA Transposable Elements; D004330:Drosophila / Q000196:embryology* / Q000235:genetics*; D029721:Drosophila Proteins; D051717:Fushi Tarazu Transcription Factors; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics*; D009154:Mutation; D014157:Transcription Factors / Q000235:genetics*
D004251:DNA Transposable Elements; D029721:Drosophila Proteins; C063459:En protein, Drosophila; D051717:Fushi Tarazu Transcription Factors; D018398:Homeodomain Proteins; D014157:Transcription Factors; C497169:ftz protein, Drosophila