A scientist created a mutation in the gene that encodes the Cactus protein to ma

Question

A scientist created a mutation in the gene that encodes the Cactus protein to make a Cactus protein that cannot be phosphorylated by Tube/Pelle (Mutant A). They also created a mutation that made a Cactus protein that is unable to bind to the Dorsal protein (Mutant B). Unfortunately, they weren't paying attention one day and forgot to label the vials containing the mutant flies. To solve the mystery of which vial contained mutant A flies and which vial contained mutant B files, they decide to perform in situ hybridization for snail expression. Describe the pattern of gene expression of snail that would be expected for these two mutants, explaining why the mutations in the Cactus protein would cause this expression pattern

Explanation / Answer

Dorsal is a nuclear transcription factor and one of the dorsal-ventral polarity genes of Drosophila. active in the mother fly. It is retained in cytoplasm by cactus protein which masks its nuclear localization signals. Tube/pelleA phosphorylates cactus and release dorsal which can move back to nucleus and initiate transcription of it target genes. One of its target gene is Snail.

So in mutant A cactus cannot be phosphorylated. so dorsal cannot move back to nucleus to initiate transcription and hence snail gene is not transcribed and snail protein is not expressed.

In Mutant B dorsal -cactus binding is inhibited. so dorsal is free to move to nucleus and initiate transcrition of snail. hence mutant B expresses snail.

Thus in situ hybridization for snail expressionwill give more signal in mutant B compared to mutant A

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