You have found a mutant mouse that does not express gene K in pancreatic beta ce

Question

You have found a mutant mouse that does not express gene K in pancreatic beta cells. You sequence gene K in the mutant and there are no mutations in the transcribed region or promoter. Southern blot using probes to regions around your gene reveals that there is a 9kb deletion 70kb away from gene K. You perform RT-PCR to look at expression of other genes near gene K. You find that there are 5 genes near gene K that are transcribed in beta cells from normal animals but not expressed in the mutant cells. There are 4 genes on the other side of the deletion from gene K that are not expressed in mutants or wild type mice. Provide an explanation for why gene K is not expressed in the mutant beta cells.

Explanation / Answer

The 9Kb of DNA that was 70kb away from the gene K and found to be deleted in the mutant must be the enhancer region. Enhancer is the region in the DNA that is bound by the activators to increase the rate of transcription.

The 5 genes near gene K that are expressed in the normal animals and not expressed in the mutants must be the conserved non-coding sequences. This region of the DNA is evolutionarily conserved and occupy the non-coding region. They are found to be helpful in regulating gene expression. They are vital sites for evolutionary divergence because mutations in these sites will lead to regulation of conserved genes resulting in gene expression that is species specific. They are cis-acting regulatory elements.

The 4 genes present on the other side of the deletion from gene K might belong to the region of silencers. As they are not expressed in both wild type as well as in mutants, the repression of gene expression would not occur in both the cases. Non-expression of these 4 genes may not be causing any change in the expression of gene K. In other words, this part seems to be not influencing the gene expression due to its absence in wild type and mutant making no difference in gene expression.

Therefore, gene K is not expressed in mutant beta cells due to the absence of 9kb sequence and non-expression of 5 genes near gene K.

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