Analyze the Data 6-2: Using RNAi RNA interference (RNAi) is a process of post-tr

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Analyze the Data 6-2: Using RNAi

RNA interference (RNAi) is a process of post-transcriptional gene silencing mediated by short double-stranded RNA molecules called siRNA (small interfering RNAs). In mammalian cells, transfection of 21–22 nucleotide siRNAs leads to degradation of mRNA molecules that contain the same sequence as the siRNA. In the following experiment, siRNA and knockout mice are used to investigate two related cell surface proteins designated p24 and p25 that are suspected to be cellular receptors for the uptake of a newly isolated virus.

Cell Treatment                                  Number of Viruses/ml

Control                                                1 ´ 107

siRNA–p24                                         3 ´ 106

siRNA–p25                                         2 ´ 106

siRNA–p24 and siRNA–p25              1 ´ 104

siRNA to viral protein                                     1 ´ 102

C. To investigate the role of proteins p24 and p25 for viral replication in live mice, transgenic mice that lack genes for p24 or p25 are generated. The loxP-Cre conditional knock- out system is used to selectively delete the genes in cells of either the liver or the lung. Wild type and knockout mice are infected with virus. After a 24-hour incubation period, mice are killed and lung and liver tissues are removed and exam- ined for the presence (infected) or absence (normal) of virus by immunohistochemistry. What do these data indicate about the cellular requirements for viral infection in different tissues?

Tissue Examined

Mouse

Liver

Lung

Wild type

infected

infected

Knockout of p24 in liver

normal

infected

Knockout of p24 in lung

infected

infected

Knockout of p25 in liver

infected

infected

Knockout of p25 in lung

infected

normal

Tissue Examined

Mouse

Liver

Lung

Wild type

infected

infected

Knockout of p24 in liver

normal

infected

Knockout of p24 in lung

infected

infected

Knockout of p25 in liver

infected

infected

Knockout of p25 in lung

infected

normal

Probe p24 cDNA Probe p25 cDNA Control SiRNA-p24 siRNA-p25 Control siRNA-p24 siRNA-p25

Explanation / Answer

As we can see from the table that in case of the lung when p24 was knocked out virus was not able to infect the liver whereas in case of lung upon knocking out p25 the virus was unable to infect the liver cells.

Above data shows that for viral replication in the liver, the virus needs the product which p25 siRNA is degrading and in case of lung virus need the product which siRNA of p24 is degrading.

This data also shows that requirement of virus fro this replication varies from cell type to cells type

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