mars and tousled-like kinase act in parallel to ensure chromosome fidelity in Drosophila

<p>Abstract</p> <p>Background</p> <p>High levels of <it>Hepatoma Up-Regulated Protein </it>(<it>HURP</it>) and <it>Tousled-Like Kinase </it>(<it>TLK</it>) transcripts are found in hepatocellular carcinoma. <it>HURP </it>overexpression induces anchorage-independent growth of 293-T cells and enhances a rough-eye phenotype resulting from <it>tlk </it>overexpression in <it>Drosophila</it>. In addition, both HURP and Mars, a <it>Drosophila </it>HURP sequence homologue, promote polymerization of mitotic spindles. Thus, the genetic interaction of <it>mars </it>with <it>tlk </it>might be required for accurate chromosome segregation.</p> <p>Methods</p> <p>To reveal whether chromosome fidelity was decreased, the frequency of gynandromorphy, an individual with both male and female characteristics, and of non-disjunction were measured in the progeny from parents with reduced <it>mars </it>and/or <it>tlk </it>activities and analyzed by Student's <it>t</it>-test. To show that the genetic interaction between <it>mars </it>and <it>tlk </it>is epistatic or parallel, a cytological analysis of embryos with either reduced or increased activities of <it>mars </it>and/or <it>tlk </it>was used to reveal defects in mitotic-spindle morphology and chromosome segregation.</p> <p>Results</p> <p>A significant but small fraction of the progeny from parents with reduced <it>mars </it>activity showed gynandromorphy and non-disjunction. Results of cytological analysis revealed that the decrease in chromosome fidelity was a result of delayed polymerization of the mitotic spindle, which led to asynchronous chromosome segregation in embryos that had reduced <it>mars </it>activity. By removing one copy of <it>tousled-like kinase </it>(<it>tlk</it>) from flies with reduced <it>mars </it>activity, chromosome fidelity was further reduced. This was indicated by an increased in the non-disjunction rate and more severe asynchrony. However, the morphology of the mitotic spindles in the embryos at metaphase where both gene activities were reduced was similar to that in <it>mars </it>embryos. Furthermore, <it>tlk </it>overexpression did not affect the morphology of the mitotic spindles and the cellular localization of Mars protein.</p> <p>Conclusion</p> <p>Chromosome fidelity in progeny from parents with reduced <it>mars </it>and/or <it>tlk </it>activity was impaired. The results from cytological studies revealed that <it>mars </it>and <it>tlk </it>function in parallel and that a balance between <it>mars </it>activity and <it>tlk </it>activity is required for cells to progress through mitosis correctly, thus ensuring chromosome fidelity.</p

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