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  • Title: How does the fushi tarazu gene activate engrailed in the Drosophila embryo?
    Author: Lawrence PA, Pick L.
    Journal: Dev Genet; 1998; 23(1):28-34. PubMed ID: 9706691.
    Abstract:
    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.
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