https://drive.google.com/open?id=1Y8MNVll-HoRpXTdxzCCzYSxy5e47cEMJ Attached is a
ID: 215922 • Letter: H
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https://drive.google.com/open?id=1Y8MNVll-HoRpXTdxzCCzYSxy5e47cEMJ
Attached is a research paper: A System of Repressor Gradients Spatially Organizes the Boundaries of Bicoid-Dependent Target Genes. Chen et al, Cell 149,618-629 (2012), Figure-by-figure details are not necessary; please however, discuss relevant background, the major findings of the work, and the experimental techniques used This is a research based question....please disscuss the question above (The link to the pdf of the paper is below)Explanation / Answer
Relevant background
It was discussed earlier that Protein gradients exist in many developing systems but it is not clear how many concentration thresholds can be provided by a single gradient, or how gradients contribute to the robust systems that ensure body plan consistency within species.
In Drosophila at the top of a network of transcription is the Bicoid (Bcd) gradient, which is formed by diffusion from a localized RNA source near the anterior pole.It was suggested that Bcd functions as
a morphogen. Differential binding sensitivity to Bcd is not the primary design principle that positions Bcd-dependent expression boundaries.
Experimental Techniques used:
In this experiment genetic experiments to significantly flatten the Bcd gradient were used to test the Bcd morphogen hypothesis. Then Bcd concentration was altered by changing bcd gene copy number. All six tested target genes viz. otd, ems, btd, gt,Hb, Kr formed were activated by less Bcd than the amounts present at their boundary positions in wild-type embryos. A systems approach was described to better understand the Bcd-dependent patterning system. Method also includes use of bioinformatics, chromatin immunoprecipitation (ChIP)-Chip data and in vivo reporter gene assays to collect and verify 66 Bcd-dependent enhancers and sequence mining to identify overrepresented motifs that correlate with boundary positioning. It was showed that Run functions with Cic and Kr to limit Bcd-dependent activation and that repression is required for correctly ordering target gene boundaries.
Major Findings of work
In this paper 66 Bcd-dependent regulatory elements were analyzed and showed that their boundaries are positioned primarily by repressive gradients that antagonize Bcd-mediated activation.
Run-binding activity is sufficient for repression of type I enhancers
Run is required for boundary positioning of multiple Bcd target genes
A major repressor is the pair-rule protein Runt (Run), which is expressed in an opposing gradient and is necessary and sufficient for limiting Bcd-dependent activation. Run functions with the maternal repressor Capicua and the gap protein Kruppel as the principal components of a repression system that correctly orders boundaries throughout the anterior half of the embryo.
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