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Regulation of segment polarity genes in the head region of different arthropods

dc.contributor.advisorWimmer, Ernst A. Prof.
dc.contributor.authorNtini, Evgeniade
dc.titleRegulation of segment polarity genes in the head region of different arthropodsde
dc.contributor.refereeWimmer, Ernst A. Prof.
dc.subject.dnb570 Biowissenschaften, Biologiede
dc.description.abstractengHead segmentation in insects, as reflected by the model system Drosophila melanogaster, is less well understood in comparison to the trunk. While the gnathal segments (mandibular, maxillary, labial) are patterned in a way similar to the trunk, distinct molecular mechanisms underlie the metamerization of the anterior head region into the procephalic (ocular, antennal, intercalary) segment anlagen (reviewed in Rogers and Kaufman, 1997). In that context, actually a unique mode of establishment for each of the procephalic segments has been suggested based on anterior head segment-specific cross-regulatory interactions among segment polarity genes (Gallitano-Mendel and Finkelstein, 1997). So far it remains unclear how the establishment of the procephalic segment polarity gene expression is controlled, although a functional input from the head gap-like genes has been elucidated and a second level of regulation in patterning of the anterior head region has been implicated (Crozatier et al., 1999).In this thesis, a bottom-up approach was employed to identify key components of the head segmentation gene network by the detection and functional dissection of cis-regulatory regions of the segment polarity genes wingless, hedgehog (hh) and engrailed in Drosophila and in a comparative approach also in the short-germ band red flour beetle Tribolium castaneum. During this study an intercalary-specific cis-regulatory element (ic-CRE) of Dm_hh was isolated, which further supports the theory of a unique establishment of each procephalic head segment. In silico analysis on the ic-CRE sequence identified a recognition site for the HLH-COE factor Collier. This binding site is essential for the function of the ic-CRE that also depends on collier activity. DNA-binding specificity of Collier to this endogenous sequence was further supported in vitro. Therefore, Collier directly controls expression of the segment polarity gene hh. Since collier itself is activated by the head gap-like gene buttonhead (Crozatier et al., 1999), Collier functions as a second order regulator in patterning of the intercalary segment.Furthermore, the ic-CRE also integrates temporal control; nested dissection led to the isolation of HMG-box binding sites required to ensure the early onset of expression. Regarding the means of restricting positive Collier activity to the posterior part of the intercalary segment, the effect of a physical interaction between Collier and the bZIP factor CncB was examined. The in vitro results indicate that CncB antagonizes DNA-binding of Collier to its target sequence, which is also reflected in vivo by a negative regulatory aspect of CncB misexpression on the ic-CRE-mediated expression. Moreover, functionality of the ic-CRE is exerted in vivo only in combination with the endogenous hh promoter, but not with a TATA-box basal promoter. This result indicates that the intercalary-specific transcriptional control of hh involves an enhancer-promoter specific interaction. However, the molecular basis of this mechanism remains to be further
dc.contributor.coRefereeBucher, Gregor Prof.
dc.subject.topicMathematics and Computer Sciencede
dc.subject.enghead developmentde
dc.subject.engsegment polarity genesde
dc.affiliation.instituteBiologische Fakultät inkl. Psychologiede

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