In mice a reduction in the expression of the Sortin Nexin 27, (SNX27) gene resul

Question

In mice a reduction in the expression of the Sortin Nexin 27, (SNX27) gene results in synaptic dysfunction in the brain. The expression of human SNX27 (cytogenetic location: 1q21) is reduced in Down syndrome patients although there is no mutation in the SNX27 gene, and this reduction may be a cause of some of the mental defects in Down syndrome patients (Wang etal. 2013, Nature Medicine 19, 473-480). One hypothesis is that this reduction in SNX27 in Down syndrome patients is caused by an increase in the amount of the negative regulatory RNAi molecule miR-155, (cytogenetic location: 21q21.3). You have been asked to determine whether miR-155 is increased in Down syndrome patients.

a. Describe what test or tests you would do, and how you would do them.

b. What results would you would expect if this hypothesis about miR-155 is correct?

c. Briefly explain why you think your results support the hypothesis.

Explanation / Answer

a. ANS: The tests are mainly needed for analysing neuropathological performance of cortex and hippocampus through immunohistochemistry and western blot analysis for the localized expression to identify Down syndrome over expression protein at both cellular and receptor level Snx27, GluR1(glutamate) , NR1 (obligatory NMDA receptor subunit protein) that mediate excitotoxicity followed by neuronal death and -actin. In order to determine miR-155 is increased in Down syndrome patients, the following test should be performed by taking suitable mouse strains from postnatal isolated brain hippocampal slices for examination:

siRNA, miRNA (microRNA) mimic and quantitative Real-Time polymerase reaction followed by promoter luciferase assay and further followed by examining the pharmacological products of cycloheximide, proteasomal action and lysosomal inhibitors action on synaptosomal and PSD fractions from mouse hippocampus. Cell surface biotynilation assay and electrophysiology experiment to denote the changes in excitatory post synaptic potential. Statistical analysis performed.

b. ANS: If this hypothesis about miR-155 is correct, by finally comparing those animal results with human results of Down’s syndrome regarding the level of impaired learning and memory in Snx27+/ mice followed by level of impaired crucial mechanism of miR-155 induced synaptic transmission and synaptic plasticity in Snx27+/ mice.

c. ANS: In order to assess the hypothesis correct as if the there is completely devoid of Snx27 may result in extremely neuronal death followed by eventual lethality in mice. Finally these changes are making hard to determine the impact of miR-155 influence on Snx27 and associated memory deficits and synaptic function during Down’s syndrome.

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