Disease relevance of gt

• We conclude that Giant Fibre morphogenesis normally relies on fasciculation with its major motorneuronal target [1].

High impact information on gt

• CtBP-dependent activities of the short-range Giant repressor in the Drosophila embryo [2].
• There are at least three short-range gap repressors in the precellular Drosophila embryo: Krüppel, Knirps, and Giant [2].
• The misexpression of Giant in ventral regions of transgenic embryos results in the selective repression of eve stripe 5 [2].
• A stripe5-lacZ transgene exhibits an abnormal staining pattern in dCtBP mutants that is consistent with attenuated repression by Giant [2].
• The restricted activity of Knirps, in contrast to that of Giant, suggests that not all short-range repressors possess identical activities, consistent with recent findings showing that short-range repressors act through multiple pathways [3].

Biological context of gt

• We describe the regulated expression of the segmentation gene giant (gt) during early embryogenesis [4].
• Gene dosage studies indicate that different thresholds of the bcd gradient might trigger hb and gt expression, resulting in overlapping but noncoincident patterns of expression [4].
• This comparative approach, coupled with the analysis of reporter gene expression in gap mutant embryos suggests that the Kr and gt proteins establish the anterior and posterior borders of h stripe 5, respectively, through spatial repression [5].
• These interactions, typical of the cross-regulation previously observed among gap genes, confirm that gt is a member of the gap gene class whose function is necessary to establish the overall pattern of gap gene expression [6].
• We tested the ability of endogenous Giant to repress when bound close to the transcriptional initiation site and found that Giant effectively represses a heterologous promoter when binding sites are located at -55 bp with respect to the start of transcription [7].

Anatomical context of gt

• We also show that the gap repressor Giant (GT) initially establishes a posterior expression limit at PS9, which shifts posteriorly after the blastoderm stage [8].
• To study short-range transcriptional repressors in cultured cells, we created chimeric tetracycline repressors based on Drosophila transcriptional repressors Giant, Drosophila C-terminal-binding protein (dCtBP), and Knirps [3].
• To investigate any interactions between the Giant Fibre and the tergotroachanteral motorneuron, we arrested the growth of the motorneuron's medial neurite by targeted expression of a constitutively active form of Dcdc42 [1].
• Hemolin from the Giant silkmoth, Hyalophora cecropia, identified as a bacteria-inducible molecule and a member of the immunoglobulin superfamily, is present as protein and transcripts in oocytes and embryos [9].

Physical interactions of gt

• Here, we present evidence that Giant might also interact with dCtBP [2].

Regulatory relationships of gt

• We demonstrate that posterior stripe boundaries are established by gap protein repressors unique to each stripe: h stripe 5 is repressed by the giant (gt) protein on its posterior border and h stripe 6 is repressed by the hunchback (hb) protein on its posterior border [10].

Other interactions of gt

• Finally, gt is required for repression of zygotic hb expression in more anterior regions of the embryo [11].
• The anterior border of Kr, which lies 4-5 nucleus diameters posterior to nuclei that express gt mRNA, is set by a threshold repression mechanism involving very low levels of gt protein [11].
• In contrast, gt activity is required, but not sufficient for formation of the anterior border of eve stripe 2, which lies adjacent to nuclei that express gt mRNA [11].
• Our previous work has described the development of the Giant Fibre in early metamorphosis and the involvement of the shaking-B locus in the formation of its electrical synapses [1].

References