The Torso signaling pathway modulates a dual transcriptional switch to regulate tailless expression

The Torso (Tor) signaling pathway activates tailless (tll) expression by relieving tll repression. None of the repressors identified so far, such as Capicuo, Groucho and Tramtrack69 (Ttk69), bind to the tor response element (tor-RE) or fully elucidate tll repression. In this study, an expanded tll expression pattern was shown in embryos with reduced heat shock factor (hsf) and Trithorax-like (Trl) activities. The GAGA factor, GAF encoded by Trl, bound weakly to the tor-RE, and this binding was enhanced by both Hsf and Ttk69. A similar extent of expansion of tll expression was observed in embryos with simultaneous knockdown of hsf, Trl and ttk69 activities, and in embryos with constitutively active Tor. Hsf is a substrate of mitogen-activated protein kinase and S378 is the major phosphorylation site. Phosphorylation converts Hsf from a repressor to an activator that works with GAF to activate tll expression. In conclusion, the GAF/Hsf/Ttk69 complex binding to the tor-RE remodels local chromatin structure to repress tll expression and the Tor signaling pathway activate tll expression by modulating a dual transcriptional switch

Bending the Rules of Transcriptional Repression: Tightly Looped DNA Directly Represses T7 RNA Polymerase

From supercoiled DNA to the tight loops of DNA formed by some gene repressors, DNA in cells is often highly bent. Despite evidence that transcription by RNA polymerase (RNAP) is affected in systems where DNA is deformed significantly, the mechanistic details underlying the relationship between polymerase function and mechanically stressed DNA remain unclear. Seeking to gain additional insight into the regulatory consequences of highly bent DNA, we hypothesize that tightly looping DNA is alone sufficient to repress transcription. To test this hypothesis, we have developed an assay to quantify transcription elongation by bacteriophage T7 RNAP on small, circular DNA templates ∼100 bp in size. From these highly bent transcription templates, we observe that the elongation velocity and processivity can be repressed by at least two orders of magnitude. Further, we show that minicircle templates sustaining variable levels of twist yield only moderate differences in repression efficiency. We therefore conclude that the bending mechanics within the minicircle templates dominate the observed repression. Our results support a model in which RNAP function is highly dependent on the bending mechanics of DNA and are suggestive of a direct, regulatory role played by the template itself in regulatory systems where DNA is known to be highly bent

Predicting white matter targets for direct neurostimulation therapy

A novel depth electrode placement planning strategy is presented for propagating current to distant epileptic tissue during direct neurostimulation therapy. Its goal is to predict optimal lead placement in cortical white matter for influencing the maximal extent of the epileptic circuit. The workflow consists of three fundamental techniques to determine responsive neurostimulation depth lead placement in a patient with bilaterally independent temporal lobe epileptogenic regions. (1) Pre-implantation finite element modeling was used to predict the volume of cortical activation (VOCA). This model estimated the electric field and neural tissue influenced surrounding two adjacent active depth contacts prior to implantation. The calculations included anticipated stimulation parameters. (2) Propagation of stimulation therapy was simulated pre-implantation using the VOCA model positioned in the subject's diffusion tensor imaging (DTI) determined 8 h post-ictally compared to an interictal DTI. (3) Validation of the predicted stimulated anatomical targets was determined 4.3 months post-implantation using subtracted activated SPECT (SAS). Presurgically, the modeling system predicted white matter connectivity and visual side-effects to stimulation. Post-implantation, SAS validated focal blood flow changes in ipsilateral occipital and frontal regions, and contralateral temporal lobe. This workflow demonstrates the feasibility of planning white matter–electrode placement with individual specificity to predict propagation of electrical current throughout an epileptic circuit