During development, Krox24 is a gene expressed in specific region of developing
ID: 101021 • Letter: D
Question
During development, Krox24 is a gene expressed in specific region of developing brain. Krox24 expression is activated by Retinoic acid bound to its cognate receptor – RAR (Retinoic Acid Receptor) and the co receptor RXR (Retinoid X receptor). Retinoic acid activity is controlled through a set of binding proteins and degradative proteins. One of the negative regulators of retinoic acid signaling is cyp26. Cyp26 binds to retinoic acid and promotes degradation of retinoic acid. Vit. D signaling causes repression of Cyp26 expression by vit D bound to its cognate receptor – VDR (vitamin D receptor) and coreceptor RXR.
In an embryo, RAR gene is mutated in its DNA binding domain leading to recognition of sequence elements that are recognized by VDR. Which of the following choices reflect the best outcome of gene expression in this embryo.
Retinoic acid level is higher than control, Krox 24 expression is upregulated, Vit-D regulated gene expression is unchanged and Cyp26 expression is reduced.Explanation / Answer
When the DNA binding domain of RAR gene is mutated leading to recognition of sequence elements by VDR can cause elevation of Cyp26. This repression is also caused by the VitD bound to its cognate receptor and coreceptor RXR. The mutation also leads to no binding of retinoic acid to RAR by which Krox 24 expression is not activated.
The outcome of this event in the gene expression in the embryo would be
The retinoic acid level is lower than control, Krox 24 expression is reduced, Vit-D regulated gene expression is unchanged and Cyp26 expression is elevated.
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