Analyze the Data 6-2: Using RNAi RNA interference (RNAi) is a process of post-tr
ID: 199790 • Letter: A
Question
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
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
D. By performing Northern blots on different tissues from wild-type mice, you find that p24 is expressed in the liver but not in the lung, whereas p25 is expressed in the lung but not the liver. Based on all the data you have collected, propose a model to explain which protein(s) are involved in the virus entry into liver and lung cells. Would you predict that the cultured mouse cells used in parts (a) and (b) express p24, p25, or both proteins?
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-p25Explanation / Answer
Knockout of p24 in the liver resulted in normal tissue, without getting infected. This indicates that p24 in expressed in liver. Knockout of p25 in the lung resulted in normal tissue, without being infected. This means p25 is expressed only in lungs. P24 is used as receptor in liver, and p25 is used as the viral receptor in lungs. In normal cultured cells, both p24 and p25 can act as the viral receptor protein.